--- The weather is too cold _____ March this year.  

--- It was even _____ when I came here years ago.

A．for; colder

B．in; cold

C．in; hot

D．for; hotter

起泡剂的作用有（）。

A、以上都不正确

B、降低气泡的运动速度，增加气泡在矿浆中停留时间

C、增大气泡机械强度，提高气泡的稳定性

D、使空气在矿浆中分散成小气泡，并防止气泡兼并