she thik it is boring 过去式 think 和 is 为什么?

要变.宾语从句的从句时态必需与主句的时态保持一致.如果主句用过去式,则从句要用相应的过去式.比如：He said I was doing my homework.
所以这个句子变成过去式是：She thought it was boring.
只有当从句是客观事实的时候才不需要变,比如说 the sky is blue,the earth is round 等等这种永恒的东西,时态都是一般现在时