在许多国家，葬礼上穿黑色是一种习俗。

In many countries it is the ___convention to wear black at funerals.

年轻一代常常挑战社会的习俗。

Younger generations often challenge social ___convention.

见面时握手的习俗在许多文化中都很常见。

The ___convention of shaking hands when meeting is common in many cultures.