21．At _______ dawn we started, but we didn’t get to our destination after sunset, so we had to feel our way in ______ dark.
A. /, the B. the, the C. / , / D. the, /
22. -- Are you familiar with the music?
-- Yes. There was a time _______ this kind of music was quite popular.
A. that B. when C. with which D. about which
