单选题 He ______ working till he was seventy years old.
A. kept up B. kept on
C. kept to D. kept out

【正确答案】 B
【答案解析】[解析] 本题测试keep动词短语的用法。keep up：持续， keep on,继续做某事；keep to；遵循，不偏离；keep out：留在外面。根据句意只有B为正确选项。句子的意思是：“他一直工作到七十岁。”