清管器漏气较为严重时，一般采取（）来处理
A.增加推球压力
B.倒推回发球点
C.发第二个球
D.放空引球
参考答案：C
识读剖面的顺序是什么
Ron can type five forms of a test in 4 hours. Joan can type the same five forms in 6 hours. If they work together, how many hours would it take them to type ten forms of a test
