Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.
Protons and neutrons have nearly equal mass and size, but protons carry a positive electrical charge, while neutrons carry no charge at all. Protons and neutrons are bound together by the strong nuclear force, one of the four basic forces in the universe. Protons and neutrons give atoms some of their most basic properties. Elements are defined by two numbers: their atomic number, which is equal to the number of protons they have, and their atomic weight, which is equal to total number of their neutrons and protons. In most lighter atoms, the number of neutrons and protons is equal, and the element is stable. In heavier atoms, however, there are more neutrons than protons, and the element is unstable, eventually losing neutrons through radioactive decay until a neutral state is reached.
Electrons are negatively charged particles. They are bound to their atoms through electromagnetic attraction. Opposite electrical charges attract one another, so the positive charge of the proton helps to keep the negatively charged electron in orbit around the nucleus of the atom. Electrons are different from neutrons in that they cannot be broken down into smaller particles. They are also far smaller and lighter than neutrons and protons. An electron is about one thousandth of the diameter of a proton and an even smaller fraction of its mass. Electrons circle the protons and neutrons at the center of the atom in orbits. These orbits are often called electron shells. The closer the orbit is to the center of the atom, the lower its energy is. There are seven electron shells, and each higher level can hold more electrons than the previous shell. Electrons naturally seek to occupy the lowest shell possible. So, if there is space in a lower shell, an electron will drop down to occupy that space. At temperatures higher than a few hundred degrees, electrons will gain energy and move to a higher shell, but only momentarily. When the electrons drop back down to their natural shell, they emit light. This is why fires and other very hot objects seem to glow.
Electrons are also primarily responsible for many of the chemical properties of atoms. Since electrons seek to occupy the lowest electron shell possible, they will move from one atom to another if there is a space available in a lower electron shell. For example, if there is an atom with an open space in its third shell, and it comes into contact with an atom with electrons in its fourth shell, the first atom will take one of these electrons to complete its third shell. When this happens, the two atoms will be chemically bonded to form a molecule. Furthermore, atoms sometimes lose electrons in collisions with other atoms. When this happens, the radio of protons and electrons in the atom changes, and therefore, the overall electrical charge of the atom changes as well. These atoms are called isotopes, and they have significantly different chemical properties from their parent atoms
According to the passage, all of the following are true of electrons EXCEPT __________.
A. they are elementary particles and cannot be broken down
B. they are considerably smaller than neutrons or protons
C. their energy levels are fixed and unchanging
D. they are kept in orbit by electromagnetic attraction
Giải bởi qa.haylamdo.com
Chọn C
Kiến thức: Đọc hiểu
Giải thích:
Theo đoạn văn, tất cả những điều sau đây đều đúng với các electron NGOẠI TRỪ __________.
A. chúng là các hạt cơ bản và không thể bị phá vỡ
B. chúng nhỏ hơn đáng kể so với nơtron hoặc proton
C. mức năng lượng của chúng là cố định và không thay đổi
D. chúng được giữ trong quỹ đạo bởi lực hút điện từ
she got the salary last week, she has complained that she is out of money
Since our train leaves at 10.30, it is _______that everyone be at the station no later than 10.15
In this course, students receive _______ in the basic English grammar
Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 33 to 37.
When you first arrive in a foreign culture, often your first reaction is completely positive. Everything seems exciting, different and fascinating. It’s an (33)______. If you are just on a short holiday, you will probably never leave this phase.
(34)_______, if you stay longer, your attitude can start to change. As you start to realize (35)_____ little you really understand the new culture, life can get frustrating. People misunderstand what you are trying to say, or they may laugh at you when you say something incorrectly. Even simple things, like posting a letter, can seem very difficult to you. Thus, you are likely to get angry or upset when things go wrong.
With time, though, you start to (36)______ to become more comfortable with the differences and better able to handle frustrating situations. Your (37)______ of humor reappears. Finally, you may feel enthusiastic about the culture once again, enjoy living in it, and even prefer certain aspects of the culture to your own.
(Adapted from Navigate – Coursebook, OUP 2015)
Điền ô 36
Mark the letter A, B, C or D on your answer sheet to indicate the word(s) CLOSEST in meaning to the underlined word(s) in each of the following questions
Our team must develop a new strategy in order to deal with the serious problem
Mark the letter A, B, C or D on your answer sheet to indicate the word(s) OPPOSITE in meaning to the underlined word(s) in each of the following questions
The band had an outstanding performance at the Grand Theatre last night
