[問題]天山4-Q41

[joni]

[Q41]
Antractica receives more solar radiation than does any other place on Earth, yet the temperatures are so cold and the ice cap [url]is reflective, so that little polar ice melts during the summer; otherwise[/url], 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 that little of the polar ice melts during the summer; were it to do so,

Ans: B
為何A錯? 另外請教"were it to do so"之意與用法?

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