Nick stayed up really late last night. So this morning he        by the time the class began.

A. had fallen asleep            B. had showm up              C. had realized

为满足造渣制度要求，对原燃料必须有如下基本要求（）。

A、含硫低

B、难熔和易熔组分低

C、钾、钠含量低

D、含铁低