2 Mary and Mark _____ (to do) their homework from 2 p.m to 8 p.m yesterday.

Решение:

Для образования прошедшего времени глагола 'to do' с подлежащим 'Mary and Mark' (они) используется форма 'did'.

2 Mary and Mark did their homework from 2 p.m to 8 p.m yesterday.