时态 1.People enjoy living (live) in large cities.

enjoy+doing

enjoy是在这里及物动词，后面接动名词，living

enjoy
1. 欣赏;享受;喜爱[+v-ing]
I enjoyed reading these books very much.
我很喜欢读这些书。
Tom doesn't enjoy going to school.
汤姆不喜欢上学。
I very much enjoyed the party.
我非常喜欢这次聚会。
I enjoy songs such as this one.
我欣赏像这首一样的歌。
2. 【书】享有(利益、权利、声誉等)
We enjoy free medical care.
我们享受免费医疗。
I enjoy good health.
我身体很健康。
3. 使过得快活;使得到乐趣[+oneself]
Are you enjoying yourself?
你玩得高兴吗?

people enjoy living in large cities.
people enjoy to live in large cities

living
因为有enjoy doing这个固定搭配