阅读理解
A poor farmer had a friend who was famous for the wonderful apples he grew.
One day, his friend gave the farmer a young apple tree and told him to take it home and plant it. The farmer was pleased with the gift, but when he got home, he did not know where lo plant it.
He was afraid that if he planted the tree near the road, strangers would steal the fruit. If he planted the tree in one of his fields, his neighbors would come al night and steal some of the apples. If he planted the tree near his house, his children would take the fruit.
Finally he planted the tree in his woods (树林) where no one could see it. But without sunlight and good soil, the tree soon died.
Later the friend asked the farmer why he had planted the tree in such a poor place. "What's the difference?” the farmer said angrily. "If I had planted the tree near the road, strangers would have stolen the fruit. If I had planted the tree in one of my fields, my neighbors would have come at night and stolen some of the apples. If I had planted it near my house, my own children would have taken the fruit.”
"Yes," said the friend, "but at least someone could have enjoyed the fruit. Now you not only have robbed (抢夺) everyone of the fruit, but also you have destroyed (摧毁) a good apple tree!"
为直流电源，
为浸透饱和氯化钠溶液和酚酞试液的滤纸，
为电镀槽．接通电路后发现
后，使c、d两点断路．下列叙述正确的是（ ）
