羊毛的细度与羊毛的品质有什么关系？

某工厂生产一批玩具，完成任务的80%后，又增加了280件，这样还需要做的玩具比原来的多20%，原来要做多少件玩具？

Mrs Smith ______ a teacher. But she doesn't do that job now. [ ]

A. used to be

B. was used to be

C. has been

D. was used to doing

简述学科活动的长处和局限。

汽车高速行驶时空气阻力可忽略不计。

双层运输汽车专用车上、下层端渡板弯曲、变形每米不大于（）

A.7mm

B.8mm

C.9mm

D.10mm