题目

根据短文内容，从短文后的选项中选出能填入空白处的最佳选项，选项中有两项为多余选项。 Once upon a time, there was a selfish man.   51   He could not share his things with anyone, not even his friends or the poor. One day, the man lost thirty gold coins. He went to his friend’s house and told him how he lost his gold coins. His friend was a kind man. As his friend’s daughter was coming from shopping, she found thirty gold coins.   52   The girl’s father told her that the gold coins belonged to his friend and he sent for (派人去叫)h如图甲是某种有保温功能的家用电热水壶及铭牌．内部电路如图乙所示，当S闭合时，接通电源，电热水壶正常工作．当水烧开时，开关S会自动断开，电热水壶自动进入保温状态，调节开关P，可调节不同的保温功率．求：（1）加热电阻丝的电阻R1的阻值．（2）当调节P使保温电热水壶的保温功率为55W时，保温电阻丝R2接入电路中的有效电阻阻值和保温电阻丝两端的电压．