宇航员永远无法从黑洞中逃脱，因为它的引力太强了。

Astronauts can never escape from a ___black hole because its gravitational pull is too strong.

我的钥匙似乎掉进了沙发这个黑洞里，怎么找都找不到。

My keys seem to have fallen into the couch ___black hole and are nowhere to be found.

那次高烧后，我的记忆中出现了一个黑洞。

After that high fever, there was a ___black hole in my memory.