The settlement is home to nearly 1,000 people, many of __ left their village homes for a better life in the city.

A．whom

B．which

C．them

D．those

锅炉安全阀设置唇边结构，主要是为了（）。

A.增加开启压力

B.降低开启压力

C.减少气压降低量

D.保证开启稳定