— How long are you staying?

— I don't know.  ________.  [      ]

A. That's OK  

B. Never mind

C. It depends  

D. It doesn't matter

下列属于阳离子型表面活性剂的是（）。

A、羧酸盐

B、磺酸盐

C、硫酸酯盐

D、铵盐类