never once has the old couple quarreled with each other since they were married 40 years ago.

问题描述:

never once has the old couple quarreled with each other since they were married 40 years ago.
这个句子怎么理解,为什么用完成时态,

这是一个固定句型,since did,have done 从句意上来理解,是从过去一直到现在,符合完成时.
就是从他们40年前结婚开始这对老夫妻之间从来没有吵过架.