52．John did his homework last night．(用at nine o'clock last night替换last night)

John 　　　　　　　　　　his homework at nine o'clock last night．

51．The boy was riding a bike when the UFO landed? (对划线部分提问)

　　　　　 　was the boy 　　　　　when the UFO landed?

50．Ted saw an alien yesterday．(改写为一般疑问句)

　　　　 　　Ted 　　　　　an alien yesterday?

49．You should come here by bike．(改为否定句)

You 　　　　　　　　　　here by bike．

48．They will go to Beijing on vacation next week．

They will have enough time．(合并为含if的复合句)

They will go to Beijing on vacation next week 　　　　　they 　　　　　enough time．

47．Mr. Wang told us, “We will have a long holiday．”(改写为间接引语)

Mr. Wang told us 　　　　　　　　　　have a long holiday．

46．I was watching TV when Mother came in．(用while替换)

　　　　　 　I was 　　　　　TV，Mother came in．