可在句子播放一遍后按暂停，复述出听到的内容，并核对以下答案。建议再次播放跟读，确保发音标准。

21 The history of economics is a tricky subject to study.

22 Sea levels are expected to rise during next century.

23 There won’t be any space for me in the car.

24 Read the fitness center instructions before attempting to use the equipment.

25 The books are filled with drawings of machines invented when he was a student.

26 It is necessary to solve the equation to determine the unknown variable.

27 The book is informative but it could be accused of political bias.

28 The burning of fossil fuels leads to pollution and global warming.

29 My siblings and I were waiting for my mother to come back from the hospital.

30 I am wondering if cell phones are actually just as dangerous as cigarettes.

31 For human beings breathing is a symbol of life.

32 Some young people seem to be addicted to their cell phones.

33 Humans have the ability to mentally say over 700 words a minute.

34 The trip for professional training will start soon, so pack the items before we leave.

35 Professor Gordon just called me a few minutes ago.

36 His objection to including scientific evidence has brought a lot of criticism to him.

37 The country’s economy is primarily based on tourism.

38 Students who wish to apply for an extension should approach their tutors.

39 We want to attract the very best students regardless of their financial circumstances.

40 We will need to make sure the school principal knows about the changes.