选择正确答案 through microscopes people can see objects that ___ t
选择正确答案 through microscopes people can see objects that ___ to the naked eye.
选择正确答案
Through microscopes people can see objects that ___ to the naked eye.
(a)invisible (b)the invisible (c)are invisible (d)are the invisible
[请解释为何要选那个答案]