48.每76年 every 76 years

47.采取措施解决问题

take measures to solve the problem

46.在接下来的十年里 in the next ten years

45.环境污染　 environmental pollution

44.重力原理　 the Law of Gravity

43.代替　 instead of

42.五岁的儿子　 a 5-year-old son

41.用完　 use up

40.是…样子 what was … like?

39.听起来像人的声sound like a human voice