Do you know_________books are made? A.what B.why C.which D.how

Do you know_________books are made? A.what B.why C.which D.how
Do you know_________books are made? A.what B.why C.which D.how

Do you know_________books are made? A.what B.why C.which D.how
A what
what ..be made 由什么材料制成的
不明白的再问.

D.how 书是怎么出来的 其余的都讲不通