求解一题GWD，，，帮下，，，先谢谢

chaomat1988

GWD3-Q10:
Antarctica receivesmore solar radiation than does any other place on Earth, yet the temperaturesare so cold and the ice cap is reflective, so that little polar ice meltsduring the summer; otherwise, the water levels of the oceans would rise 250feet and engulf most of the world’s great cities.
A.   is reflective, so that little polar icemelts during the summer; otherwise,
B.   is so reflective that little of the polarice melts during the summer; were it to do so,
C.   so reflective that little polar ice meltsduring the summer, or else
D.   reflective, so that little of the polar icemelts during the summer, or
E.    reflects so that little of the polar icemelts during the summer; if it did

chaomat1988

thx

steve_chem

if it were to do so= were it to do so

chaomat1988

我选了A。。答案是B，，，   后面那个WERE IT TO DO SO，是什么啊 虚拟语气吗？  求高人指点