补全对话。

A: Mum, (1) ______ is my baseball?

B: Sorry, I don't (2) ______.Is it (3) ______?

A: No, my book is on the chair,but my baseball isn't.

B:  Is it (4) ______?

A:  No, there's nothing (没有任何东西) in my backpack.

B:  Is it (5) ______?

A: Umm…Oh, yes! It's here! It's under my quilt (被).Thank you,Mum!

B:  You're welcome.

柴油机的活塞广泛采用（）制造。

A、铸铁

B、铸铝合金

C、铸铝

D、铸钢