15 minutes做主語時(shí),謂語動(dòng)詞用單數(shù).這是要遵循主謂一致的原則,詳細(xì)見如下解釋,
表示時(shí)間、距離、度量、重量、金額等的復(fù)數(shù)名詞作主語,被看作整體時(shí),謂語動(dòng)詞用單數(shù)；若強(qiáng)調(diào)個(gè)體也可以復(fù)數(shù).如：
Twenty years is a long time.
二十年是很長時(shí)間.
Two kilometers is a long way to go on foot.
步行兩千米是一段很長的路程.
Six months have passed,and we still have no news of them.
六個(gè)月過去了,我們依然沒有他們的消息.
比較：
Ten dollars is too much for this old coin.
這個(gè)古幣沒有10塊錢這么高的價(jià)格.
Three dollars were paid for the old coin.
那個(gè)古錢花了3塊錢.
Twenty years is a long time.
20年是一段很長的時(shí)間.
Twenty years have passed since they got married.
他們結(jié)婚已有20年了.