--- Is her sister a teacher or a student?
--- .
A:No, she's a teacher
B:No, she isn't a teacher
C:She's a student
D:Yes, she's a teacher
图甲:玻璃珠被加热后,小灯泡发光.说明____;
图乙:半导体二极管D接入电路,小灯泡发光,调换电池的正负极后,小灯泡不发光.这说明____.