【请教】有一道关于BE TO DO 的题目

和凝日火

Between 14,000 and 8,000 B.C. the ice cap that covered northern Asia, Europe, and America began to melt, uncovering vast new areas that were to be occupied by migrating peoples moving northward.

A. began to melt, uncovering vast new areas that were to be occupied

B. began melting, to uncover vast new areas to be occupied

C. began, by melting, to uncover vast new areas for occupation

D. began, after melting, uncovering vast new areas which are to be occupied

E. would begin to uncover, through melting, vast new areas for occupation

答案：A

我不太明白，我印象里是说GMAT认为be to do不能用来表示未来或者义务，要用will或者should，但是答案是A，所以这个说法是正确的吗？

wl女友

我也想问