泵控型半闭式液压系统通常是从主泵()。
A.低压侧泄油和补油
B.高压侧泄油和补油
C.高压侧泄油,低压侧补油
D.排出侧泄油,吸入侧补油
参考答案:A
如果等差数列{an}中,a3+a5=12,那么a4=[ ]
A.12
B.24
C.6
D.4
Much attention should ______ the environment and fighting against pollution.
A.be paid to protect
B.pay to protecting
C.pay to protect
D.be paid to protecting