Helen ______ her keys in the office so she had to wait until her husband ______ home.

A．has left; comes

B．left; had come

C．had left; came

D．had left; would come

为了对某欧式看涨期权定价，其标的资产为股票WX，理财师小张经过仔细测算，给出以下定价公式：
C₀=S₀×0.56-xe^-rT×0.43
若某机构卖出与这份看涨期权具有相同标的股票、执行价格和期限的看跌期权N份，现在机构准备对冲风险，应该进行的操作是______。(其中1份期权对应的股票交易数量为100股。)

A．购买44N股WX股票
B．购买56N股WX股票
C．卖空44N股WX股票
D．卖空56N股WX股票