as good as gold 很乖，很听话，（小孩）规规矩矩的，乖巧的

【例句】
The children caused no trouble all day; they were as good as gold.

一整天孩子没惹过一点麻烦，他们乖极了。

His little daughter is as good as gold. she's never been as rebellious as other children.

他的小女儿很乖，从不像别的孩子那样不听话。