Parenting education in particular is crucial to the development of a child , as the tenure (a growing child spends with parents since the inception of life) is( crucial to the development of child ),   when children develop cognitive abilities and sense awareness towards their varying environments. 

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【个人观点】as，后面不是原因状语从句,而是比较状语从句,第一个括号里边是定语，第二个括号里边是表语，是比较对应项，必须省略。括号里边是我的补全内容。

句子的意思没什么难的，但是有个问题，when 这个状语从句是哪个句子的状语？

有三种情况，第一是修饰主句，第二是修饰从句。第三种情况是两个一块修饰，相当于both of them are crucial, when...