启动换热器时应（）。
A、先开冷流
B、后开热流
C、先开热流
D、后开冷流
参考答案：A, B
This is _____ mother, and _____ name is Mary. [ ]
A. her, she
B. my, her
C. your, his
D. his, his
疖的产生原因是（）
A．湿热火毒内蕴
B．肝火妄动，湿热熏蒸
C．暑湿阻于肌肤
D．暴气毒邪，袭于皮肤，传注经络
E．寒痰凝滞
