We must study harder, ______ we'll not pass the exam. [ ]
A. and
B. but
C. or
D. so
答案:C
颤动线区不应位于()
A.硬软腭交界处的软腭上
B.硬软腭交界处之后约1~2mm
C.硬软腭交界处之后约2~3mm
D.硬软腭交界处之后约3~4mm
E.硬腭区
叙述高性能混凝土的配制。