按照惯例，由主席致开幕词。

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

因此，教师拥有更长的假期是惯例。

So it is ___customary that teachers have longer holidays.

在许多文化中，客人带一份小礼物是习俗。

In many cultures, it is ___customary for guests to bring a small gift.