keep后面加原形还是—ing形式？

ing形式。

keep to 有另外的意思，没有加原形的说法，以下是keep to的意思。
待在
I kept to my tent.
我一直待在帐篷里。
紧靠向
If you keep to the main road you won't get lost.
假如你沿着主干道走, 就不会迷路。
(使)谈话不离题
In discussing this problem, we ought to keep to the point at issue.
讨论这个问题时, 我们应该抓住分歧点。
(使)遵守〔坚持〕
The tourists insist on keeping to their plan.
旅行者坚持按旅行计划行事。
保密; 不交际
There are only a man and his wife living there.They keep entirely to themselves.
只有一个人和他的妻子住在那里, 他们完全不与外人来往。
将…的数量限制在
I don't want too many people to come to the party.Please keep the guests to about fifty.
我不想让太多的人来参加晚会。把客人控制在50位左右吧!

通常来说是加动词的ing形式

keep doing sth