下列属于生物圈范围的是[ ]
A.大气圈上层,水圈和岩石圈上层
B.大气圈下层,水圈和岩石圈上层
C.大气圈,水圈和岩石圈上层
D.大气圈,水圈和岩石圈
答案:B
单向流
They will not start the work _______ their teacher comes back.
A.while
B.until
C.as soon as
D.if