利用干电池、导线、小灯泡、电动机、铅笔芯、橡皮、塑料尺探究：（1）物质导电性；（2）电动机转向；（3）电磁感应；（4）电阻与长度的关系。能够完成的实验个数有（  ）

阅读短文，回答问题

One afternoon, Mrs. Green’s husband wanted to catch the 3: 30 flight to London to have an important meeting. She was very surprised when he telephoned her at     5 o’clock and said that he was still at the airport.

“What happened to you? ” asked Mrs. Green.

“Well, ” said Mr. Green, “Everything was going fine. I got my ticket, checked my bag and waited in line. I walked across the runway(跑道) to the airplane and I saw my friend Jack Scott, who was an airplane engineer. I shouted to him and a policeman caught me. ”

“Why did he catch you? ”

“I don’t know, ” said Mr. Green, “As soon as he heard my shout, he ran towards me and caught me. ”

“What did you shout to your friend? ”

“All I said was ‘Hi，Jack’. You know that’s the usual way we say hello to our friends. ”

“But you don’t know the sentence ‘Hi, Jack’ also means to take control(控制) of a plane by force(武力). ”