Đề thi thử THPT Quốc gia năm 2017 môn Tiếng Anh trường THPT chuyên Đại học Vinh lần 1 có đáp án

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 (cosmic rays 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.

In the past, it was common for three or more (14) ______to live together in the same roof. Nowadays most elderly people live (15) _______their own. They generally stay in contact with their children or grandchildren but might live in the different part of the country. People also live longer, often 20 years after they have (16) ______ from their job. Modern American culture tends to value youth rather than age. This create an interesting challenge for older people and for the country.

American families also have troubles. They are the divorce rate, the fact that working mothers might have (17) ______ time with their children, and the problems that parents and children sometimes misunderstand each other. (18)_______, family is still at the center of most people's lives.

A little more than a hundred years ago, a number of European scholars began to record stories being told in peasant cottages and compile them into the first great collections of European folk tales. Written evidence exists to prove that the folk tales they recorded existed long before then though. Collections of sermons from the 12th to the 15th century show that medieval preachers knew of some of the same stories as those recorded by the 19th century folklorists.

The collections of folk tales made in the late 19th and early 20th centuries provide a rare opportunity to make contact with the illiterate masses who have disappeared into the pass without leaving a trace. To reject folk tales as historical evidence because they cannot be dated and situated with precision like other historical documents is to turn one's back on one of the few points of entry into the previous centuries. But to attempt to penetrate that world is to face a daunting set of obstacles, the greatest of which is the impossibility of listening in on the story tellers. No matter how accurate they may be the versions of the tales recorded in writing cannot convey the effects that the storytellers must have used to bring the stories to life: the dramatic pauses, the sly glances, the use of gestures to set scenes, and the use of sounds to punctuate actions. All of those devices shaped the meaning of the tales, and all of them elude the historian. He cannot be sure that the limp and lifeless text he holds between the covers of a book provides an accurate account of the performance that took place in earlier times.