— Talking loudly in a library is impolite.
— In fact, we should also ________ not to cough(咳嗽) or sneeze（打喷嚏）loudly in public.
A：look after
B：be careful
C：take care of
D：look up
含有杂质的镁2.4g放入一定量盐酸中，得到0.202g氢气，该镁中可能混有的杂质是
若函数f（x）=2ax2﹣x﹣1在（0，1）内恰有一个零点，则a的取值范围是（ ）
