Mrs Smith's living room is large. There is a television in the room. The television is near the window. There are some magazines on the television. There is a table in the room. There are some newspapers on the table. There are some armchairs in the room. The armchairs are near the table. There is a stereo in the room. The stereo is near the door. Mrs Smith often listens to music from it.

算一算。

7元5角-1元=____           2元+10元=____              15元-7元=____     

6元5角+2角=____          1元-1分=____                2元8角-2角=____     

2元-8角=____               7元+3元9角=____           3角+5分=____    

在探究凸透镜成像规律的实验中，当烛焰、凸透镜、光屏处于图中所示位置时，恰能在光屏上得到一个清晰的像。利用这种成像原理可以制成（    ）