在下面括号里填写合适的数． 99m3=______dm3 56cm3=_____

自身免疫性疾病易迁延复发，试阐述其可能的免疫发病因素。

幼儿急疹发病多见于（）

A.春夏季

B.春秋季

C.冬春季

D.夏秋季

E.秋冬季

Preventer bars are fitted on lifeboat releasing hooks to prevent（）.

A.the falls from unhooking if the releasing gear is operated accidentally while the boat is being lowered

B.operation of the release lever until the boat is waterborne

C.the falls from rehooking after they have been released

D.accidental unhooking when the falls become slack

公共关系学并不是一门独立的学科。（）