进电灯开关的线，应采用（）。
参考答案：火线
容易变形的图形是[ ]
A．直角三角形
B．平行四边形
C．等腰三角形
Occasions are quite rare _____ I have the time to spend a day with my kids. [ ]
A. who
B. which
C. why
D. when
