57. Measures should be taken to _______(阻止) the earth from being _______(污染).

56. Mary is such a _________(漂亮) girl as we all love.

55.　 Seeing the teacher enter the room, the students _______(假装) to read the books.

54.　 The students are under great ____________(压力).

53.　 __________(按) the red button in case of fire.

52．____________(总统) Obama came into power.

51.　 The people __________(出席) at the meeting showed great interest in his lecture.

50.　 Make good __________(准备) for the coming NMET.

49.　 The students are well ___________(准备) for the coming NMET.

48.　 When he was a small boy, he _________(较喜欢) walking to cycling.