GWD4-Q28 求问 or else

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 not 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

我觉得是因为or else不适合表达虚拟。the water levels of the oceans “would” rise明显采用了虚拟语气。

B。is so reflective that little of the polar ice melts during the summer; were it not to do so,

C。so reflective that little polar ice melts during the summer, or else

yet the temperatures are so cold and the ice cap （缺少谓语）so reflective