i stood there patiently until he ----- his work

除非有上下文,要不然had finished 和finished 语法上都没问题
这两个动作谁先谁后呀.
你这问题问的好
用he had finished 就有他做完了,你还stood there 的含义,就是说,他先“做完”
直接用finished就没有这时间的差别的含义,可以是同时完成的意思