老师我知道operating marigns 在三年之内基本持平 不是一个warning sign.但是我不明白为啥 increasing in operating margins 会是一个warning sign. 不要说 这是一个结论，请解释一下怎么会得到这个结论的。
Increases in operating margins can be a warning sign of potential overstatement or non-sustainability of operating and/or net income. In this case, however, operating margins for Construction Supply have been relatively constant during the last three years.
