净化厂产生爆炸的原因大体有()种。
A.两
B.三
C.四
D.五
参考答案:A
—Bill, can I use your dictionary? I left mine at home.
—Of course you________. Glad to help you.
A.need
B.may
C.must
D.can
土烧失量试验,重复灼烧称量,至前后两次质量相差小于(),即为恒量。
A.0.2mg
B.0.3mg
C.0.4mg
D.0.5mg