如图所示，矩形线框abcd的一边ad恰与长直导线重合(互相绝缘)．现使线框绕不同的轴转动，能使框中产生感应电流的是  

A．绕ad边为轴转动  

B．绕oo′为轴转动  

C．绕bc边为轴转动

D．绕ab边为轴转动

1.Passage 1
It is a pleasure to be here today to commemorate the first Earth Day with you by looking through this "Window on the American Environment". While I have not yet viewed the television series, from the accompanying book I can see that it is a very ambitious effort. The producers have interviewed a large number of environmental leaders in the United States, from early founders back in the 1970s through those involved in the contemporary movement. //
I am sure you will hear many different opinions, because the diversity of the American environmental movement is part of its strength. The ability of individuals and non-governmental organizations to express their opinions and make their voices heard in the press and in the electoral process is the root of the movement and why it flourishes today. I vividly remember going outdoors with my elementary school class on Earth Day 1970 to examine our environment by looking at what grew in the pond behind our school. The motto of that first Earth Day was "think globally, act locally", and our young teacher wanted us to better understand what was right around us. //
Nowadays teachers have access to all sorts of wonderful educational materials to help students study the environment and learn about concepts like biodiversity, climate change and protection of the ozone layer that were still foreign to us in 1970. But we knew then about toxic chemicals, deforestation, water pollution—the subject of our pond study—and land use issues, and we were learning to understand how much of an impact these could make on our futures. //
Earth Day 1970 was a novel idea proposed by individuals—not a government—that grew on its own, so that in that very first year, over 20 million Americans participated. We said, "think globally", but Americans were not yet thinking as much beyond their borders as we do today. Equally it would have been unimaginable in 1970 that China would air a 22-part television series on the United States. It would be another two years before the images of President Nixon’s famous trip to China would be broadcast on our television screens in the United States and we started to have the opportunity to learn about each other. //
Today the United States and China have a great deal to celebrate together for Earth Day. We are working together in areas from water conservation to the protection of endangered species to the development of new, cleaner sources of energy. We have an active program to work with Beijing to support its goal of a Green Olympics in 2008. Together we are researching climate change and exploring the possibilities for using hydrogen and fusion as energy sources. The United States government, through agencies like the Environmental Protection Agency, the Department of Energy, the Fish and Wildlife Service, the National Parks Service and dozens more has an active program of cooperation with its Chinese counterparts. //