手动起重机用的焊接链条其安全系数不得小于15。
参考答案:错
Mr. Irving, who ____ in a high school for forty years, is now living in retirement. [ ]
A. has taught
B. taught
C. had taught
D. has been teaching
男性更年期常见的临床表现有()方面
A.精神心理
B.运动能力
C.体力不支
D.性功能
E.其他