选址之初会通过对人口密度、客流量、人口流动性的测算来预计（）的程度。
A、销售能力
B、产品市场
C、购买力
D、人口密度
参考答案：D
They did everything in their power to save the building dating back to the Qing Dynasty, but their efforts were _______.
A．in turn
B．in time
C．in vain
D．in need
氯气消毒的作用主要靠HCLO（）。
