A study shows that walking fast in your old age is a that you will live a long life.A. si

问题补充：

A study shows that walking fast in your old age is a that you will live a long life.

A. sign

B. mark

C. symbol

D. signal

答案：

(答案→)A. sign

B. mark

C. symbol

D. signal

解析：此题为词义辨析题。sign迹象，征兆；mark标记，记号；symbol象征，符号；signal信号。根据题意“老了走的快是长寿的征兆”，因此选A。