79.　 The world population is e____________; it’s now more than 60 billion.

78.　 A_________ is the scientific study of the sun, moon, stars and other heavenly bodies.

77.　 Look! _________　 _________(大团的) snow and rocks are falling down the mountain.

76.　 We must start at ____________(黎明). The city is very far from here.

75.　 Whether we’ll go for a picnic ____________　 ____________(取决于) the weather.

74.　 They decided to fly to Beijing ___________　 ____________(而不是) take a train.

73.　 I have seen him ____________(在…内) these last three days.

72.　 ____________　 __________　 __________(就…) I know, his home is far from school.

71.　 He ____________　 __________ (高兴起来)at once when I promised to help him.

70.　 The heavy rain ____________ us __________(阻止) going to see a film.