theydesigntoolswithhookswhichtheyusedwhentheyarelookingforfood.theydesigntoolswithhookswhichtheyusedwhentheyarelookingforfood.换个which怎么理解,USED为什么是过去式,而后面theyare用的现在进行时?

Question

they design tools with hooks which they used when they are looking for food.
they design tools with hooks which
they used when they are looking for food.
换个which怎么理解,USED为什么是过去式,而后面they are 用的现在进行时?

Answer 1

整个句子叙述的是一般事实,所以使用一般现在时,which they used 是which引导的定语从句,修饰tools,可以更换过去式,表示以前使用过.they are looking 表示寻找食物的过程,不表示现在进行时的意思.