Một nguồn phát sóng dao động điều hòa tạo ra sóng tròn đồng tâm O truyền trên mặt nước với bước sóng λ. Hai điểm M và N thuộc mặt nước, nằm trên hai phương truyền sóng mà các phần tử nước dao động. Biết OM=8λ; ON=12λ và OM vuông góc ON. Trên đoạn MN, số điểm mà phần tử nước dao động ngược pha với dao động của nguồn O là:

A. 5

B. 6

C. 7

D. 4

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 questions from 35 to 42.

  When another old cave is discovered in the south of France, it is not usually news. Rather, it is an ordinary event. Such discoveries are so frequent these days that hardly anybody pays heed to them. However, when the Lascaux cave complex was discovered in 1940, the world was amazed.

  Painted directly on its walls were hundreds of scenes showing how people lived thousands of years ago. The scenes show people hunting animals, such as bison or wild cats. Other images depict birds and, most noticeably, horses, which appear in more than 300 wall images, by far outnumbering all other animals.

  Early artists drawing these animals accomplished a monumental and difficult task. “They” did not limit themselves to the easily accessible walls but carried their painting materials to spaces that required climbing steep walls or crawling into narrow passages in the Lascaux complex.

  Unfortunately, the paintings have been exposed to the destructive action of water and temperature changes, which easily wear the images away. Because the Lascaux caves have many entrances, air movement has also damaged the images inside. Although they are not out in the open   air, where natural light would have destroyed them long ago, many of the images have deteriorated and are barely recognizable. To prevent further damage, the site was closed to tourists in 1963, 23 years after it was discovered.

What does the passage say happened at the Lascaux caves in 1963?

A. Another part was discovered.

B. Visitors were prohibited from entering.

C. A new entrance was created

D. A new lighting system was installed.

Mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the following questions.

- “A bat can hear from a long distance ” “                                     ”

A. You bet

B. Yes, good hearer

C. No, you can be so sure

D. You know a bat well

Nêu những nét nổi bật của phong trào độc lập dân tộc ở Ấn Độ trong những năm 1929 – 1939.