prep80 时态问题求教

80. Radiocarbon dating of fossils taken from caves on islands along southeastern Alaska’s coast suggest that at least a portion of the area was remaining ice-free during the last ice age.
A. suggest that at least a portion of the area was remaining
B. suggest at least a portion of the area remaining
C. suggests that at least a portion of the area remained
D. suggests at least a portion of the area that had remained
E. suggests at least a portion of the area to have remained

错误原因：动词时态掌握的不好

A: suggest用单数

B: 同上

C: correct

D: during 要用过去时

E: during 要用过去时

我的问题：白勇的书上，这样写的：during+ the past/last/recent +时间 应该要用现在完成时（白勇书的79页），

可是为什么NN的解释说during要用过去时那？

我觉得这里的弹劾the area remained是 the area that have remained的分词形式。

不知道我理解的对不对？请指教

没人理？怎么发现prep上的题目解答的都很少？

麻烦帮助了！