a call of nature的用法和样例：
- I waked early to answer a call of nature.
- As soon as I get on a long-distance but I want to answer a call of nature.
- I was probably off the road, behind a bush, answering a call of nature.
- He signs autographs with a flourish, poses gamely before a barrage of photographers and excuses himself only briefly for a call of nature.
- I must answer the call of nature.