[求助]天山4-Q41

Q41:
Antarctica receives more solar radiation than does any other place on Earth, yet the
temperatures are so cold and the ice cap is reflective, so that little polar ice melts during
the summer; otherwise, the water levels of the oceans would rise 250 feet and engulf
most of the world’s great cities.
A. is reflective, so that little polar ice melts during the summer; otherwise,
B. is so reflective tha t little of the polar ice melts during the summer; were it to do so,
C. so reflective that little polar ice melts during the summer, or else
D. reflective, so that little of the polar ice melts during the summer, or
E. reflects so that little of the polar ice melts during the summer; if it did
答案为B

B分号之前的确实是最正确的，我的问题在于分号之后的，为什么是were it？