but no one has been able to prove that fish is any better for the brain than many other kinds of foo

题目

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?

答案

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