Đọc kĩ đoạn văn rồi chọn từ/ cụm từ thích hợp nhất trong số các gợi ý A,B,C, hoặc D để hoàn tất mỗi trong số các câu theo sau

Have you ever shouted inside a large empty building? If so, you may have heard your voice come back to you. The sound of your voice hits the walls and bounces back. What you hear is the echo of your voice. You hear echo after you have shouted. This is because it takes time for the sound to travel to the walls and back to your ear again. Sound travels very fast, even faster than a speeding aero plane. In a thunderstorm, you see lightning first. Then a few seconds later, you hear the thunder. You can tell how near or how far the storm is by the length of time it takes for you to hear the thunder. If you hear it very soon after you see the lightning, the storm is very close. Many animals use their eyes to find their way. However, some animals such as bats, cannot see very well. Their ears are much better than their eyes, so they use their hearing to find their way. Since insect-eating bats are almost blind, they send out high sounds as they fly. These sounds bounce off anything in the bat's way. The bat's ears then pick up the echo. The echo tells the bat the safest direction to fly in. The echoes also bounce off insects in the air, so the bat knows where to find its food.

76. An echo is _____.

A. sound that large buildings make. B. time that sound takes to travel.

77. During a thunderstorm, we_____.

A. see the thunder first. B. hear the lightning first. C. see the lightning first. D. hear the thunder first.

78. It takes time for the sound of thunder to travel to our _____.

A. ears B. eyes C. nose D. mouth

79. Bats use echoes to _____.

80. Sounds from bats _____.

B. chase other insects. D. warn other insects of the coming bats.