The features of the floor of the Kasei Valles on Mars look just like those at the base of Antarctic ice streams, so it suggests that possibly it was flowing ice that carved the giant Martian channels previously attributed to cataclysmic floods.

(A) so it suggests that possibly it was flowing ice that
Wrong. Pronoun problem.

(B) a suggestion that flowing ice may have
Wrong. "a suggestion" sounds inappropriately here. We should use verb-ing modifier if we want to give more information about the preceding clause.

(C) to suggest flowing ice as possibly having
Wrong. Meaning problem. "to suggest" conveys purpose meaning. <-- wrong meaning.

(D) suggesting that flowing ice may have
Correct. Verb-ing modifier --> modifies the previous clause correctly.

(E) which is suggestive of flowing ice having possibly
Wrong. "which" modifies ice streams wrongly.

Hope it helps.
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Yes and in this case, this observation is applicable. The subject "the features" (of the floor of the Kasei Valles on Mars) are the ones that are the basis of the suggestion.

it is hard. why choice B is wrong?
choice B mean
that the features of floor A look like the feature of floor B is a suggestion that the flowing ice make the chanel
choice D mean

that the features of floor A look like the feature of floor B suggests that the flowing ice makes the channel

I prefer D but why choic E is wrong.