铆钉的破坏现象最常见的是钉杆被剪断和（）。
参考答案：孔壁承压破坏
We are allowed _____ part-time jobs after school. [ ]
A. having
B. to have
C. had
D. to having
模板DNA的变性温度是（）。
A.22℃左右
B.72℃左右
C.55℃左右
D.94℃左右
E.100℃左右
