A:沿轨迹BC自由下落
B:沿轨迹BD继续运动
C:沿轨迹BE做匀速直线运动
D:沿轨迹BF继续上摆
(2015.•广东佛山)I don't understand why more girls ________ to do housework than boys in today's society.
说说蚕吐丝前的一些现象,以及蚕农应该做些什么准备呢?