国防建设是国家为提高（）而进行的各方面的建设。
A.国防实力
B.军队战斗力
C.国家经济
参考答案：A
Tom has _____ in the English contest _____ all the students he works the hardest. [ ]
A. come out the first; because
B. come up first; because of
C. come out first; because of
D. come up the first; because
汽轮机发生叶片断落时，一般有以下特征？
