在一桶含盐10%的盐水中加进5千克食盐，溶解后，桶中盐水的浓度增加到20%，桶中原来有多少千克盐？

Nowadays it is not uncommon for a big, p schoolboy to elbow an elderly woman aside in the dash for the last remaining seat on the bus or tube, () stand up and offer his seat to her.

A. much less

B. not to mention

C. not to say

D. rather than