NN们：
2. Those who have visited the Grand Canyon have typically(有特色的) seen layers of sediment in the gaping canyon, with different colors that mark the passage of time like the rings in a tree trunk.
(A) seen layers of sediment in the gaping canyon, with different colors that mark
(B) see layers of sediment in the gaping canyon, whose different colors mark
(C) been seeing layers of sediment in the gaping canyon, whose different colors are markers of(D) been able to see layers of sediment in the gaping canyon, with different colors marking
(E) seen layers of sediment in the gaping canyon, marking by different colors
问题1：在这里为什么要用been able to see,而不用seen呢？
问题2：with different colors marking 与marking by different colors 区别在什么地方？作者: himba 时间: 2004-10-6 19:10
问题1
be able to 是一个优选标志，有就选吧～
问题2
这两个的重心变了发现没有，要保持原句的结构～
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