题目

正电荷Q位于如图所示的坐标原点，另一负电荷 –2Q放在何处才能使P（1,0）点的电场强度为零（      ） A．位于x轴上，x >1         B。可以不在x轴上 C．位于x轴上，0 < x <1      D。位于x轴上，x < 0   答案：DYesterday the police were joined by more than 20 volunteers in the continuing search for the two missing teenagers, Vicky Gray and Tom Hunter, and their guide, Gavin Jones. The police said that they had disappeared during an adventure tour of Cape York Peninsula.This was the second day of the search and the police were now very worried about the safety of the three missing people.The police said that the search had covered a wide area, but the rain forest was thick and their work was made harder by the recent rain. Later on Chief Inspector (警官) Roger Fleet said, “The travellers had a radio with them. If they had been in trouble, they would have called us.”The three travellers left Cooktown very early on Saturday morning in a Toyota car. They took a small dirt road that runs down to the Daintree River, a dangerous river full of crocodiles (鳄鱼). Chief Inspector Roger Fleet said the tourists wouldn’t have got into trouble if they had stayed on the main road.A photo of Vicky and Tom was found by a policeman under the “Be Careful about crocodiles” sign near the river. Why was the photo left behind? This is just one of the unanswered questions. Other questions are: Why was the photo left behind? Why was the Toyota parked and locked at the edge of the rain forest? The police said that the travellers had left a map of the area behind. Why? Why had someone drawn a cross on the point where the car is? Is this a sign? What does it mean? If anyone can give information or has seen these three young people, contact the local police in Cooktown.1.This article is probably taken from ___________A. a newspaper B. a magazine C. a storybook2.Which word best describes the search of the three missing people?A. Helpless B. Hard C. Successful3.Which of the following things wasn’t found by the police?A. A touring map. B. A photo of the travellers. C. The travellers’ radio.4.All the following are unanswered questions except_____________.A. why they left a photo behindB. why they came to this areaC. why their Toyota was parked in the place5.The article asks people to _____________.A. join the police in searching for the missing peopleB. tell the police about the travellers’ ages and their appearanceC. provide information about the missing people