78. Mary is eighteen years old.(改為同義句) 

Mary is girl.

77. I like singing. My sister likes singing,too.(合并成一個句子) 

My sister and I singing.

76. Study hard,and you'll pass the English exam. (改為同義句)

 study hard, pass the English exam.

75. Huang Lei isn't as good at tennis as Larry.(改為同義句) 

Larry is tennis Huang Lei.

74. It will be fine tomorrow. They will go to the park.(改為含有條件狀語從句的復合句) 

If it fine tomorrow,they to the park.

73. He has shorter legs than Sam.(改為同義句) 

His legs are than.

72. There's going to be an English speech contest next week.(改為同義句) 

  an English speech contest next week.

71 . The problem is so hard that he can't solve it.(改為同義句) 

The problem is hard for him solve.

70. Wang Tao is the tallest boy in our class.(改為同義句) 

Wang Tao is   student in our class.

69. I went to school on foot yesterday.(改為一般疑問句)

 you to school on foot yesterday?