Unit 7 DCABA BACDA AC
　　新概念英语第4册课后习题:
　　Multiple choice questions 多项选择题
　　Choose the correct answers to the following questions.
　　Comprehension 理解
　　1 What happens if you shout on a mountainside?
　　a.You will be able to measure distance.
　　b.Nothing.
　　c.It will take a long time for an echo to come back.
　　d.You will hear an echo.
　　2 You can measure the depth of the sea by ____.
　　a.shouting so you get back an echo
　　b.tapping on the hull of a ship
　　c.working out how long it takes to get an e ...