在历史小论文《我眼中的邓小平》中，某同学写道：“我心目中的邓小平是一个外交家。他活跃于国际舞台，在他努力下，中美关系开始正常化，中英建交并顺利解决香港问题。”对于这段文字，下列评语中比较恰当的一条是（）

      Traffic lights are very important for us. I think you know this. But do you know how they were born?
      Garrett A. Morgan was the father of traffic lights. He was an American. His family was very poor. He left school at the age of 14. He was clever. He always looked for better ways to do things. And he liked to make new things.
      At that time, every American wanted to have a car. The streets were full of cars. The traffic was really bad. “Why not put three lights at each corner ? They should be red_,green_,and yellow，” Morgan said , “ Let them tell cars to go or stop.” He made a timer (定时器)to change the lights.
     So we have traffic lights today .

为探究电磁铁的磁性与哪些因素有关，小丽所在实验小组通过交流与合作设计了以下实验方案：用漆包线（表面涂有绝缘的导线）在大铁钉上绕若干圈，制成简单的电磁铁．如图所示的a、b、c、d为实验中的四种情况．根据小丽的猜想和实验，完成下面填空：

（1）在实验中小丽是通过观察比较____ 来判断电磁铁磁性强弱的．

（2）通过比较____ 、____ 两种情况，可以得出的结论是：电磁铁磁性的有无与电流的有无有关（选填“a”、”b”、“c”或者“d”）．

（3）通过比较 b、c两种情况，可以得出的结论是：____ 

（4）通过比较d中甲、乙两电磁铁，可以得出的结论是：____