多级离心泵主要用在流量不很大，但扬程相对（）场合。
A.小
B.中等
C.一般
D.较大
参考答案：D
下列生物与其所属的类群配对正确的是 [ ]
A．松树 被子植物
B．猎豹 脊椎动物
C．铁线蕨 苔藓植物
D．蚯蚓 脊椎动物
Is _________ 48 hours _________ the man-made satellite _________ is made in our country to orbit the planet around?
A．it; that; where
B．it; when; that
C．it for; that it takes; that
D．it; that it takes; which
