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 ？（）

A.A

B.B

C.C

D.D

E.E

“哲学要是不同科学接触，就会变成一个空架子”。这句话的意思是说 [ ]

A．哲学是各门具体科学的基础

B．哲学以各门具体科学为基础

C．哲学是各门具体科学的总和

D．哲学是世界观，各门具体科学是方法论