______ the call for help, the boys immediately rushed out to see what was going on.

A．In order to hear

B．Hearing

C．Having heard

D．They heard

某一住宅使用石灰厂处理的下脚石灰做粉刷，数月后粉刷层多处向外拱起，还出现一些裂缝。

试分析造成此现象的原因是（）。

A.石灰中掺杂质太多

B.石灰没拌制均匀

C.石灰中含有大量的欠火石灰

D.石灰中含有大量的过火石灰