她走得那么快，我跟不上她。

She was walking so fast I couldn't ___keep ___up ___with her.

不幸的是他太快了，我跟不上他。

Unfortunately he was too fast and I couldn't ___keep ___up ___with him.

徒步时，我不得不跑步才能跟上队伍。

I had to run to ___keep ___up ___with the group during the hike.