---When facing some challenges, Jimmy shows great courage.

--- Yes. He is a man who never _________.

A．goes on

B．gives up

C．runs out of

D．gives back

( )的成分要求比较严格，与灰口铸铁相比，它的含量较高，通常在4.5%～4.7%的范围内变动。

A．球墨铸铁

B．蠕墨铸铁

C．可锻铸铁

D．耐磨铸铁