Our English teacher is very nice.We _____ friends since three years ago.A.were B.became C.have

答案应该是 have been
时间状语是 since years ago ,是现在完成时的标志.become 是短暂性动词,不能和一段时间连用,所以用延续性动词 have been .
意思是：我们的英语老师很好.自从三年以前我们就是朋友了.havemade 中 make 是短暂性动词，不能和 since years ago 连用。