题目

阅读理解 It is named a kind of woodenEiffel Tower, because of the fact that there was a large wooden platform far outin the lake on which stood an improbably high diving board. It was,I'm sure, the county's tallest wooden structure and no one had ever been known tojump from it. So it was quite a shock whenour teacher, Mr. David,announced that he would dive off the high board that very afternoon. Word of his questionableplan was already spreading through town as Mr. David swamout to the platform. Hewas just a tiny, stick figure when he got there but evenfrom such a distance the high board一闭合圆线圈，放在随时间均匀变化的磁场中，线圈平面和磁场方向垂直，若想使线圈中的感应电流增强一倍，下述方法可行的是（　　）A．使线圈匝数增加一倍B．使线圈面积增加一倍C．使线圈匝数减少一半D．使磁感应强度的变化率增大一倍