题目内容：

SAT语法题,
Some scientists believe that mentally stimulating activities may increase the number of brain cells （available to replace if any） are lost through aging.请问维护森么括号里的要改成available to replace any that,我不是很明白!

优质解答

注意断句噢.
brain cells (省略了个that) available to ... -- 这是个定语从句
to replace ...
any that are ... -- 又是个定语从句