when it come to后面可加动名词doing，或名词,因为这个to是介词；
例如When it comes to dancing,Im all thumbs。谈到跳舞,我真是一窍不通。
when it comes to用法
when it comes to当涉及某事(或做某事)时
When it comes to something or when it comes to doing something means when it is a question of something or doing something.
Here "to" is a preposition.
(注意：这里 "to" 是介词)
例如：
1.When it comes to getting things done, he's useless.
一涉及做事，他便不中用了。
2. Toddlers are notoriously antisocial when it comes to sharing toys.
众所周知，刚学会走路的孩子不愿和别人分享玩具。
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