请教一道语法难题。

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