—Were you at home at 9:00 last night? I called you but nobody answered.—Sorry, I ________ at that time.
A:take a shower
B:took a shower
C:was taking a shower
D:am taking a shower
如图是德国设计师设计的一个球形透镜太阳能系统,通过透镜聚光之后再发电.此透镜是一个( )