Though it is

We didn’t find the Blacks___________the lecture. —No one had told them about___________a lecture the following day.

Is the girl in the red skirt your sister?—No. She is____ classmate.

David usually takes _______ walk for an hour after dinner.

The principal is not here, and you’d better call him ______ 3 p.m. ______ 5 p.m. tomorrow. [ ]