過去進(jìn)行時。
were、was 是 be 動詞的過去時，后加了doing 成為過去進(jìn)行時。
例句：
Vendors were doing a brisk trade in souvenirs.
小販們的紀(jì)念品生意很興隆。
They were doing 70 miles an hour.
他們每小時達(dá)到70英里。