题目

已知圆柱Ω的母线长为l，底面半径为r，O是上底面圆心，A，B是下底面圆周上两个不同的点，BC是母线，如图，若直线OA与BC所成角的大小为，则= ． 答案：【答案】【解析】试题如图，过A作与BC平行的母线AD，连接OD，则∠OAD为直线OA与BC所成的角，大小为．在直角三角形ODA中，因为，所以．则．Dear Peter, How about you study? It’s Sunday today I’m writing a letter to you. I’m going to tell you .I’m going to tell you about things in Beijing.Beijing is different from London. In our country, we drive on the left side of the road, but here people drive on the right side. Most people go to work by bus or by bike. The rush hours(高峰时间) are from seven to nine in the morning and five to seven in the afternoon. People in China work around eight hours a day, five days a week. They usually begin to work at eight in the morning, and rest on Saturday and Sunday.I have Chinese classes every morning from Monday to Friday. The students in our class are from many countries. We’re all working hard and friendly. The Chinese students are ready to help us with our Chinese .We also help them a lot with their English. We’re getting along very well（相处的融洽）That’s all for today. Please write tome soon.Yours,Susan小题1:Susan is probably from_____A．ChinaB．EnglandC．AmericaD．Canada小题2:People drive on _____in London.A．the same side in Beijing asB．the right side of the roadC．the left side of the roadD．both sides of the road小题3:The rush hours a day in Beijing usually last______A．two hoursB．three hoursC．over five hoursD．about four hours