are responsible for|is responsible for|was responsible for

有时行人也对事故负责，主要是当他们匆忙的时候。

Sometimes walkers ___are ___responsible ___for accidents, mainly when they are in a hurry.

公司对环境破坏负责。

The company ___is ___responsible ___for the environmental damage.

谁应对这次事故负责？

Who ___was ___responsible ___for the accident?