--Why were you late this morning?

--I was _________ I overslept．

A．because of    B．because    C．why    D．what

-- Why were you late this morning?

-- It was _________I overslept.

[　　]

-- Why were you late this morning?

-- It was _________I overslept.

[　　]

-- _________were you late again this morning, Jack?

--Because the traffic was too heavy in the street.                 -

A. Why                 B. How                C. When               D. Where