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butnoonehasbeenabletoprovethatfishisanybetterforthebrainthanmanyotherkindsoffoodhasbeenabletoprove是现在完成进行时?

题目详情
but no one has been able to prove that fish is any better for the brain than many other kinds of food
has been able to prove是现在完成进行时?
▼优质解答
答案和解析
不是的,就是现在完成时,没有表示进行的部分啊,have done 是现在完成时嘛,只不过这里的done是be + adj.的形式而已