43. The students began to do the volunteer work last summer.
    A. The students haven’t done the volunteer work since last summer.
    B. The students have done the volunteer work last summer.
    C. The students have done the volunteer work since last summer.
    D. The students have done the volunteer work for last summer. ago.
46. The last time I went to the museum was a year ago.
        A. I have not been to the museum for a year.        B. A year ago, I often went to the museum.
        C. My going to the museum lasted a year.        D. At last I went to the museum after a year.
47. I haven’t worked in orphanages for years.
    A. I haven’t worked in orphanages for long ago.  
    B. The last time I worked in orphanages since years ago.
    C. I didn’t work in orphanages years ago.               
    D. I last worked in orphanages years ago.
48. We don’t let students smoke in the room.
A. We  don’t permit students smoke in the room.
B. We allow students to smoke in the room.
C. We don’t permit students to smoke in the room.
D. We don’t permit students smoking in the room.