猜想一：琴弦发出声音的音调高低，可能与琴弦的横截面积有关；

猜想二：琴弦发出声音的音调高低，可能与琴弦的长短有关；

猜想三：琴弦发出声音的音调高低，可能与琴弦的材料有关．

为了验证上述猜想是否正确，他们找到了上表所列4种规格的琴弦，因为音调的高低取决于声源振动的频率，于是借来一个能够测量振动频率的仪器进行实验．

①为了验证猜想一，应选用编号为____、____的琴弦进行实验；

②为了验证猜想二，应用编号为____、____的琴弦进行实验；

③表中有的材料规格还没填全，为了验证猜想三，必须知道该材料的横截面积是____mm²。

阅读理解

　Scientists say life will be very different in 2050.

    First, there will be no TV channels(频道)in 2050. People will choose a program(节目)from a computer and watch it on TV. In 2050, we will get information from the computers only.

    Second, water will be a big problem in 2050. In many places, people won't have water to drink.

    Third, cars will use new and clean fuels and they will go very fast. There will be a computer in every car. And the computers will control the cars and there won't be any accidents(事故).

下列说法正确的个数有（　　）

①射线AB与射线BA表示同一条射线．

②若∠1+∠2=180°，∠1+∠3=180°，则∠2=∠3．

③一条射线把一个角分成两个角，这条射线叫这个角的平分线．

④连结两点的线段叫做两点之间的距离．

⑤40°50ˊ=40.5°．

⑥互余且相等的两个角都是45°．