The winter of 2008 was extremely bad._____most of people say it was the worst winter of their lives.

A．In general

B．In a word

C．In all

D．In fact

为了探究电磁铁的磁性强弱跟哪些因素有关，小琴同学用漆包线（表面涂有绝缘漆的导线）在大铁钉上绕若干匝，制成简单的电磁铁，下图甲、乙、丙、丁为实验中观察到的四种情况．

①当开关闭合后，请在甲图中标出磁体的N极；

②比较图______________和______________可知：匝数相同时，电流越大磁性越强；

③由图______________可知：当电流一定时，匝数越多，磁性越强．