She _____(can)skate when she was only four.

问题描述:

She _____(can)skate when she was only four.

could;原因:后面when she was only four可以知道用过去式

could when后从句为过去完成时,所以主句谓语动词用过去分词(主过从过)

could 用can 的过去式