李老师在教学中存在这样一种令人尴尬的现象：他讲课不可谓不透、不明、不用功（有时甚至很卖力），课下督促检查不可谓不细不紧不认真，而学生也付出了较大的努力，师生满以为会取得较大的收获与提高。可最终结果却不尽如人意，付出和希冀相去甚远。

针对这种现象，结合相关理论谈谈李教师应该怎样改变这种情况。

It was now clear that no such weapons were manufactured and none been found. ()

A. was found

B. were founded

C. has been found

D. have been founded