下列地貌单元中，既属于东部季风区，又处在地势第二级阶梯的是[ ]
A、华北平原
B、黄土高原
C、河套平原
D、柴达木盆地
答案：B
They went into a small house but _____ . [ ]
A. not persons did they find
B. not a person found they
C. not a person did they find
D. not a person they found
发动机润滑系统一般由哪些零部件组成？其主要部件各有什么功用？
