从碱洗塔中流出的硫酸钠亚硫酸钠的浓度约为（）。
A.10%
B.5%
C.20%
D.15%
参考答案：A
Luckily, the poor boy had enough money _____ he could buy a train ticket.
A．by which
B．on which
C．with which
D．for which
什么是体育社会调查的程序？（重点）
