GWD13套题中的第11套为何答案非常怪异呀？

象这题：

Q29:

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.

1. is
        reflective, so that little polar ice melts during the summer; otherwise,
2. is so
        reflective that little of the polar ice melts during the summer; were it
        to do so,
3. so
        reflective that little polar ice melts during the summer, or else
4. reflective,
        so that little of the polar ice melts during the summer, or
5. reflects
        so that little of the polar ice melts during the summer; if it did

看划线的前后关系阿.

A吸收辐射,然而温度低冰盖R 小PI融化在夏季  (所以) 海平线上升250 engulf世界上大多数城市.

一开始直接排除ACD

再看BD were it to do so 明显比IF IT DID 复杂.而且IF IT DID 符合原文的意思.