customary

因此，教师拥有更长的假期是惯例。

So it is ___customary that teachers have longer holidays.

按照惯例，由主席致开幕词。

It is ___customary for the chairman to make the opening speech.

在派对上，主人迎接所有客人是惯例。

It is ___customary for the host to greet all the guests at the party.