下列说法是为了减小摩擦的是[ ]
A、自行车轮胎上有凹凸不平的花纹
B、在缝纫机的各部件上加润滑油
C、在皮带传动中,把皮带拉紧
D、刹车的闸皮选用橡皮做成
答案:B
The incomes of skilled workers went up. __________, unskilled workers saw their earnings fall. [ ]
A. Moreover
B. Therefore
C. Meanwhile
D. Otherwise
一套倾向岩层的倾向和倾角大体一致的是()。
A.水平岩层
B.倾向岩层
C.单斜岩层
D.倒转岩层