压裂中前置液的作用,主要是疏通地层,制造裂缝。()
参考答案:对
Although he has not gone to college,he shouldn't ________ studying for his degrees.
A.be prevented
B.be stopped
C.be kept from
D.be protected from
下列不属于烟气分析的主要项目的是()。
A.二氧化碳
B.氧
C.一氧化碳
D.水