摩擦力的方向与滑动的方向()。
A、相同
B、相反
C、垂直
参考答案:B
Some problems ___ in the lecture by Mr.Smith are very popular in our school, such as the waste of electricity, water and food, etc...
A.referring
B.referred to
C.referring to
D.were referred
同相比例运算电路的比例系数大于1,而反相比例运算电路的比例系数小于()。