Black Spider（蜘蛛）was having trouble catching bugs（臭虫）in his web, while Grey Spider caught two bugs in his.

    “You are so lucky,” Black Spider said to Grey Spider. “You have two bugs while I have none. It's not fair(公平的).”

    “Everyone has lucky days and unlucky days. Let's eat the bugs together,” said Grey Spider.

    Black Spider decided to join Grey Spider for lunch.

    “You must do some special things to get lucky, is it magic?” Grey Spider whispered.

    “No, build your web!” said Black Spider. “Repair your web! Enlarge your web! Make your web wider!”

    “Is that all?”

    “Yes, build a new web!” said Grey Spider.

    After lunch, Black Spider went back and made a new web. He built his web wider. Once he was done he slept all through the night because he was very tired.

    In the morning, Black Spider was excited to see four bugs in his web. He told Grey Spider about it. Grey Spider smiled at Black Spider. “By enlarging your web, you have enlarged your possibility to catch all these bugs,” Grey Spider said. “There is chance all around us. Luck is everywhere. You need to work to make it so more good luck comes your way.”

    Mrs Black lived in a city of England. Her husband died two years ago and one of her children worked in the capital and the other three lived in another town. Her husband didn't leave her much money and she had to live a simple life. Sometimes her children went to see her during their holidays，but they stayed with her for only two or three days. Luckily she had a cat with her. She liked it very much and took it everywhere she went.    One winter morning the old woman got up early. She was going to buy some food in a shop. And when she came out, she found there was much snow in the street. She had to sweep it away. And suddenly she found the cat at the corner of the house. And then she laughed .Her cat caught a big mouse.

下列叙述与地球存在生命无关的是（   ）

用伏安法测一节干电池的电动势E和内阻r，所给的器材有：

A．电压表V：0～3～15V

B．电流表A：0～0.6～3A

C．滑动变阻器R₁（总阻值20Ω）

D．滑动变阻器R₂（总阻值100Ω）

E．开关S和导线若干