专升本考试

试题来源：专升本英语-69
【单选题】 Mr. Smith ______ working till he was seventy years old.
A．kept up
B．kept on
C．kept to
D．kept out

参考答案：B
网考网解析：
keep on doing sth.意为“坚持做... 查看试题解析出处>>