Read the following passage and mark the letter A, B, C, or D to indicate the correct answer to each of the questions from 35 to 42  

     The elements other than hydrogen and helium exist in such small quantities that it is accurate to say that the universe is somewhat more than 25 percent helium by weight and somewhat less than 75 percent hydrogen.  

     Astronomers have measured the abundance of helium throughout our galaxy and in other galaxies as well. Helium has been found in old stars, in relatively young ones, in interstellar gas, and in the distant objects known as quasars. Helium nuclei have also been found to be constituents of cosmic rays that fall on the earth (cosmicrays are not really a form of radiation; they consist of rapidly moving particles of numerous different kinds). It doesn't seem to make very much difference where the helium is found. Its relative abundance never seems to vary much. In some places, there may be slightly more of it; in others, slightly less, but the ratio of helium to hydrogen nuclei always remains about the same.  

     Helium is created in stars. In fact, nuclear reactions that convert hydrogen to helium are responsible for most of the energy that stars produce. However, the amount of helium that could have been produced in this manner can be calculated, and it turns out to be no more than a few percent. The universe has not existed long enough for this figure to be significantly greater. Consequently, if the universe is somewhat more than 25 percent helium now, then it must have been about 25 percent helium at a time near the beginning.  

     However, when the universe was less than one minute old, no helium could have existed. Calculations indicate that before this time temperatures were too high and particles of matter were moving around much too rapidly. It was only after the one-minute point that helium could exist. By this time, the universe had cooled so sufficiently that neutrons and protons could stick together. But the nuclear reactions that led to the formations of helium went on for only relatively short time. By the time the universe was a few minutes old, helium production had effectively ceased.  

What does the passage mainly explain?

Read the following passage and mark the letter A, B, C, or D on your answer sheet to choose the word or phrase that best fits each of the numbered blanks from 25 to 29  

     Tourism is a big business. Millions of people around Europe spend their winters planning their destinations for the following summer, and their summers (25) ___________ to foreign climes for two weeks in the sun. They are the modern-day descendants of the aristocrats and the wealthy who would take months to complete the "Grand Tour” of Europe. But unlike their forefathers, tourists these days get a bad press. They're not (26) ___________ in the local culture, we're told they're just after the chance to behave a bit more wildly than they do at home. What's more, they damage the local environment and don't respect the locals and their way of life. 

     But are tourists really to blame? (27) ___________is it the fault of the tourist industry, which has failed to provide reasonably-priced alternatives? And if the local resort only offers a succession of bars for the tourists to visit, can we really criticize them for not doing more cultural activities? One holiday company, Far and Away, claims that tourists are crying out for more cultural holidays and believes that it has (28) ___________to come up with a range of package holidays which are affordable, culturally interesting, and environmentally friendly. Their brochure, which is to be (29) ___________ later this month, offers 200 holidays based on cultural themes, including history and architecture, learning the language, meeting the locals.

Not only my study but my hobbies also really keep me occupied every time.

It is the recommendation of many psychologists that a learner ought to use mental images to associate words and remember them.

Before giving presentation, always ___________ the focus on the projector so that everyone can read what is on the screen.

We live in a large house in ___________ middle of the village.

In the early years of the 20th century, several rebellions ___________ in the northern parts of the country.

The government issued a warning to local companies that all waste must be disposed of___________ or they will face heavy fines.

It's inevitable that there will be ___________ in the workforce over the coming months.

I don't like to ask people for help as a rule but I wonder if you could ___________ me a favor.

I extend my sincere ___________ to the family and friends of John Miller, who has suddenly left us at the age of 54.