exercise|exercises|exercising

她大多数晚上锻炼，通常是跑步。

She ___exercises most evenings, usually by running.

我和莎拉在健身房，我们正在锻炼时听到汤姆和约翰在谈论它。

I was at the gym with Sarah, we were ___exercising when we heard Tom talking about it with John.

步行是很好的锻炼。

Walking is good ___exercise.