在普通碳素钢中，随着含碳量的增加，钢材的疲劳强度（）。
A.不变
B.提高
C.下降
D.可能提高也有可能下降
参考答案：C
补全对话。
A: What do you do on weekends?
B: __1__
A: To the movies?
B: Yes, what about you?
A: __2__
B: __3__
A: Twice a week. It's pretty nice.
B: What do you do on the Internet?
A: I usually talk with my friends. __4__
B: Yes, it's 12798367.
A.__5__ We can talk on the Intetnet.
2._____________________
3._____________________
4._____________________
5._____________________
SPF鸡开产前，（）抽样，检测淋巴白血病病毒、鸡毒支原体、滑液囊支原体、鸡白痢沙门氏菌感染。
A.70%
B.80%
C.90%
D.100%
my friends. __4__