选A

本题考查分词作后置定语的两种情况：

(1)现在分词——用于主动语态：The man wearing a pair of glass is my brother.

(2)过去分词——用于被动：The earth is a planet covered by water over 50%.

可以换成相应的定语从句：

(1)The man who wears a pair of glass is my brother.

(2)The earth is a planet which is covered by water over 50%.

所以当不容易判断出来的时候，可以改为相应的定语从句。

本题换成定语从句是The wild flowers looked like a soft blanket which coversthe desert.

题中blanket是cover的逻辑主语，主动关系，所以答案是covering。