如果边际收益大于边际成本，企业就可以通过减少产量来增加利润。
参考答案：错
Mr. White came to our school in 2008, and since then he _____ us English. [ ]
A. teaches
B. taught
C. has taught
D. will teach
电磁阀的开关是通过电磁力来实现的。（）
