这句话咋么看不懂,是什么句式啊.

题目

这句话咋么看不懂,是什么句式啊.
He was almost killed when a ship he was on sank and he had to swim back to land.特别是when a ship he was on sank这里,sank不是sink的过去式么,咋么会用在on后面.

答案

He was almost killed when a ship he was on sank and he had to swim back to land.ship he was on是个从句,应该是ship which he was on省掉he was on就是when a ship sank整句话的意思是：当他所在的船沉没的时候...