同学你好，该知识点来自沪江网校《英语零基础直达大学六级【3年随心畅学班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好~
这里it是指的the wall，相当于the wall was low enough for him to climb
用they的话it也保持不变，因为指的是the wall，举个例子
The water rose high enough for them to continue upstream.
水位涨得够高了，他们可以继续向上游航行。
This house isn't big enough for us.
这房子对我们来说不够大。
The reception was a little faint but clear enough for him to receive the signal.
接收到的信号有点弱，但对他来说已够清晰，可以接收到。
The gate was too high for a man of his age to climb.
大门太高了，像他那个年龄的人爬不上去。
Her problem was just too big for her to tackle on her own.
她的问题太严重了，光靠她自己是没法解决的。

enough 和 too表达的意思不一样。
too所要强调的是“超出了正常的限度”，如：
They saw something like a cloud coming, but it was too low in the sky.他们看到像云样的东西从低空飘了过来，但太低了。
We here had too much rain lately.最近这里雨下得太多了。

enough当形容词，译为“足够的，充足的”可以放在名词前
be +adj/adv(形容词/副词) + enough for sb. to do sth 做某事对某人来说太（足够）...

祝同学学习进步~