题目

下列叙述正确的是（） A . 13C和14C属于同一种元素，它们互为同位素 B . 2H和3H是不同的核素，它们的质子数不相等 C . 14C和14N的质量数相等，它们的中子数相等 D . 6Li和7Li的电子数相等，中子数相等 答案：AHow do you like to go to school like one in Oxford, England ? There are no r_________ classes. The students go from one group to a _________ when they want to. You may find students of fourteen, sixteen or twenty-five years old all in the s_________ group. They work at their o________ studies. Nobody tells them what they should or shouldn’t be doing. The day I visited, school b_________ at nine. Some s_________ were working at a tape recorder and listening to their lessons. Others were watching TV on Maths. A group was reading in the school l________. I didn’t see anybody just sit doing n__________. Everybody was studying. At lunch time I could also see students working. They were talking a________ their lessons while they were e_________. When you think of these students you can be sure it is one of the best schools in the world.