77.　 Spaceships without people have reached other parts of the universe.

76.　 I hope I can make my own computer that way someday.

75.　 All beepers and mobile phones must be kept off during the concert.

74.　 Children under 1.2m in height cannot be taken into the concert hall.

73.　 There are twenty more trees to be planted. =There is another 20 trees to be planted.

72.　 The only problem is we can’t eat tree.

71.　 Many thousands of trees must be planted every year.

70.　 Trees in the forests can keep raindrops from hitting the soil directly, so the soil is not easily washed away.

69.　 Tie the tree to the top of the stick to keep it straight.

68.　 Put the tree in the hole so that it is straight.