The boy wanted to ride his bicycle in the street,but his mother told him_______.为什么只能填not to而不是not to do或是not to do it

在上下文明确的情况下，可以省略不定式的那个动词。

不定式作宾语补足语时，省略to后的动词部分，即用to代替整个不定式。例如：
　　(1)The boy wanted to ride his bicycle in the street?but his mot her told him not to.
　　(2)You'd better finish the job on time if he ordered you to.

可以从这角度看
原句可以写为
The boy wanted to ride his bicycle in the street, but his mother told him
not to ride his bicycle in the street.
但因为最后的 not to ride his bicycle in the street 与前面的 ride his bicycle
in the street相同
在基於不会造致意思不清楚的假设下
作者故意将重覆的字眼省去
以求精简(写作技巧之一)
因此
do 及 do it都不是答案
如果答案要用do
比较适合的是
not to do so.

not to是not to do it的缩写，所以如果你填了not to do 的话it不能没有
因此，这道题not to do it 和not to都是正确的

这是省略句,只能填not to是约定俗陈,没有道理的,外国人就这么说.
就像许多外国人爱问你们中国人问什么说是一棵树,而不是一个树的道理.
但是当后面是be/have been时,be 就不能省了
例如：Her mother wants him to be a teacher,but he doesn‘t want to be.
这里be就不能省略了.
您懂了吗?

not to 的意思是 不 加到句子里面就是 男孩想在街上骑他的自行车，但他的母亲告诉他不要。
not to do it 、not to do 的意思是 不这样做 。 认为这样会通顺么？