可用于人工主动免疫的免疫原是()。
A.佐剂
B.类毒素
C.内毒素
D.外毒素
E.抗毒素
参考答案:B
As a student, we should learn how _____ the words in the dictionary. [ ]
A. to look up
B. look up
C. looking up
柴油机进气门间隙一般取0.35mm。