as good as gold千万不要理解为“像黄金一样宝贵、一样好”；这个词组是习语，意思是“很乖”，常用来形容一个人表现很好、很乖、规规矩矩的、乖巧的，但要注意它常用来形容孩子。

【例句】
The boys were as good as gold on our walk.
我们散步的时候，这帮小男孩表现得很乖。

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。