“ ______ as often as you can,” our English teacher often tells us, “ you will make rapid progress.”

A．Practice

B．To practice

C．Having practised

D．Practising

其它条件不变，精镏塔采用温差控制时，下列说法正确的是（）。

A、温差不受塔压影响

B、温差受塔压影响小

C、只要温差正常，产品质量不受影响

D、温差正常时，产品质量随塔压升高而升高