题目

We produce 500 billion of plastic bags in a year worldwide and they are thrown away polluting oceans, killing wildlife and getting dumped in landfills where they take up to 1,000 years to decompose. Researchers have been unsuccessfully looking for a solution. The 16-year-old Canadian high school student, Daniel Burd, from Waterloo Collegiate Institute, has-discovered a way to make plastic bags degrade(降解) in as few as 3 months, a finding that won him first prize at the Canada Wide Science Fair, a ＄10,000 prize, a ＄20,000 scholarship, and a chance to revolutionize a major environmental 某同学在做练习使用示波器实验，发现示波器上显示如图甲，为了将这个波形变成如图乙所示的波形，可进行如下调节：（填旋钮或开关编号w.w.w.k.&s.5*u.c.om） （1）调节        使图象变细； （2）调节        和       使图象位于示波器显示屏的中央； （3）调节         增大波形曲线竖直方向的幅度； （4）调节         使图象从负半周开始。