It's not easy _____ a house for my pets.[ ]
A. to keep
B. keeping
C. to make
D. making
答案:C
射线探伤的质量要求,对接头的质量不低于______为合格。
A.Ⅰ级
B.Ⅱ级
C.Ⅲ级
D.Ⅳ级
由椎骨的椎体和椎弓围成的结构是
A.椎孔B.椎间孔C.椎间盘D.棘突E.横突