简易呼吸器挤压一次入肺的空气约()
A.200~300ml
B.300~600ml
C.500~1000ml
D.600~1200ml
E.1000~1500ml
参考答案:C
在CDMA1X网络中,利用()技术来有效抵抗慢、快衰落。
A.极化
B.智能天线
C.阵列天线
D.分集
.
It was _____ his mother came in _____ to prepare his lessons.
A.not until; did the boy begin
B.until; that the boy didn’t begin
C.until; did the boy not begin
D.not until; that the boy began