在拉伸应力和腐蚀介质同时作用下的腐蚀叫做()。
A、冲击腐蚀
B、腐蚀疲劳
C、应力腐蚀开裂
参考答案:C
—Where _____ she _____ on vacation?
—She _____ her uncle.[ ]
A. did, go; visited
B. does, go ;visited
C. did, went; visited
D. does, went; visit
DN20表示水管的半径等于20毫米。