题目

---It’s said that scientists have ________ a way to deal with the disease(疾病) ---Really? That’s great! A. caught up with  B. come up with  C. agreed with     D. compared with 答案：B如图所示，在原来不带电的金属细杆ab附近P处，放置一个正点电荷．达到静电平衡后，（ ）A．a端的电势比b端的高B．b端的电势比d点的低C．a端的电势不一定比d点的低D．杆内c处场强的方向由a指向b