语法与词汇 17.The students on the school bus were______for half an hour in the traffic so all of them were late for class that morning.

【正确答案】 A

【答案解析】四个选项的意思分别是：held up举起；提出；拦截，使停滞。kept off挡住，防止……接近。taken back拿回，退回。put off拖延；扔掉。根据句意，应该选择A。