当交通灯是黄灯时,我们要说:
A:It's yellow. Let's stop.
B:It's yellow. Let's wait.
一个棱长为6分米的正方体木块的体积是____立方分米.
Ann and Bruce are ____ (write) their homework.
关于以下四种光学仪器的成像情况的说法中不正确的是( )