英语中动词作主语的句子结构通常有以下几种形式：

动词原形

例句：To learn is important.

动词的现在分词形式

例句：Swimming is my favorite sport.

例句：Eating too many vegetables is good for our health.

动词不定式

例句：To eat too many vegetables is good for our health.

动词的-ing形式

例句：Doing is not so easy as saying.

例句：Flying in the sky is great fun.

例句：Sing is better than saying.

这些结构在英语中非常常见，尤其是在口语和书面语中。建议根据具体的语境和句子长度选择合适的动词形式作为主语。