甲向乙借款,乙不信任甲的还款能力,这个时候丁向乙保证,在甲不能偿还债务的时候,承担偿还债务的责任。丁的这种行为,即是()。
A.保证
B.抵押
C.定金
D.留置
参考答案:A
_____ what he can do. He might get a job tomorrow. He might stay out of work for weeks.
A.We didn’t know
B.He doesn’t know
C.There is no knowing
D.It was known that
超声的声波频率应该大于以下哪项()
A.2000Hz
B.5000Hz
C.10000Hz
D.20000Hz
E.50000Hz