帮忙看看下面的英语句子

问题描述:

帮忙看看下面的英语句子
The moon is our nearest neighbour in space,and like ourselves it is kept tied to the earth by the earth's gravitational pull.
请问kept tied to the earth

The moon is our nearest neighbour in space,and like ourselves it is kept tied to the earth by the earth's gravitational pull.
月亮太空中离我们最近的邻居,它也像我们一样,紧紧地被地球引力.
kept tied to the earth
紧紧地被地球引力tied 是什么意思?紧紧地