题目

根据句意，用所给的词组填空。 how long         how soon                  how far          how often how much      how many             how deep       how old 1. --- __________ do you go to Beijing? --- Once a year. 2. --- __________ do you want to go to Beijing again? --- I can’t wait to. 3.--- __________ is it from Nanjing to Beijing? --- About 1,157 kilometers. 4.--- __________ have you been a League member? --- Three years. 5.--- __________ will Mr. Green come back to Beijing? --- In three years. 6.--- __________  图中虚线所示为静电场中的等势面1、2、3、4，相邻的等势面之间的电势差相等，其中等势面3的电势为0．一带正电的点电荷在静电力的作用下运动，经过a、b点时的动能分别为18eV和3eV．当这一点电荷运动到某一位置，其电势能变为﹣5eV时，它的动能应为（　　）A. 8eV B. 13eV C. 15eV D. 21eV