蚊子是传播疾病的致命杀手。

Mosquitoes are dangerous ___killers that spread diseases.

蚊子是热带地区的主要致命杀手之一。

Mosquitoes are one of the main ___killers in tropical regions.

那个杀手最终被警方逮捕归案。

The ___killers were finally arrested by the police.

这个数学题真是要命，我花了两个小时才解出来。

This math problem is a real ___killer, it took me two hours to solve it.