The birth planning policy allows my parents to have a second child because of my disability,but to look after me,they chose ( )A,not to do B,not to have C,not to D,to not have one请帮忙解释下为什么---not to do,not to have,not ,not to have one不行?那么not to do so,not to have another one行吗?

C 是最简洁的答案。
A. not to do 的后面还应该有宾语
B "have" 对不上
D 语法错误。

not to do so 和 not to have another one 都可以。

not to do so, not to have one或 another one,是可以的,其余的不可以，C是省略了动宾短语 have a second child, do 是替换了have 避免重复，但是have, do 都是及物动词，不能缺宾语，所以要有后面的词作宾语。

答案应该是：C 它是语法“省略句”的一种.将C补全应该是：not to have a second child.
英语句子中不定式to后面的成分可省略,但是to必须保留.又如：
I wanted to go out to play basketball,but my mother told me not to (play basketball).
not to do so,not to have another one两个都可以.但记住：“言以简洁为贵.”