问题 选择题
如图所示,在x轴上方存在着垂直于纸面向里、磁感应强度为B的匀强磁场,一个不计重力的带电粒子从坐标原点O处以速度v进入磁场,粒子进人磁场时的速度方向垂直于磁场且与x轴正方向成120°角,若粒子穿过y轴正半轴后在磁场中到x轴的最大距离为a,则该粒子的比荷和所带电荷的正负是(  )

A.,正电荷

B.,正电荷

C.,负电荷

D.,负电荷

答案

答案:C

选择题
阅读理解

阅读理解

     Everyone's at it, even my neighbors. I thought I might be the only person left in the world who hadn't

done an eBay deal. So, I decided to try my hand at online auction (网上拍卖).

     Buying for beginners: Sign up on www. ebay. co. uk. Most items(e.g. tables, computers, and

books)ready for auction will come with a picture and a short description; others may be marked with "

Buy It Now " and have a fixed price. You can buy these right away.

     If the item is being auctioned, you offer the highest price you are prepared to pay and eBay bids

(出价)for you. The bid will be increased little by little until it goes beyond your highest bid, then you are

emailed and asked if you would like to bid again. Auctions last up to 10 days and when they finish you

get an email telling you whether you have won the item.

     How to pay: Sellers decide how they would like to be paid and you need to check this before placing a bid as you might not want to post a check or postal orders. The easiest way is through PayPal, an online payment system that takes the money away from your credit card (信用卡).

     Selling made simple: If you plan to sell on eBay, it helps to include a picture of the item. I followed

my friends' advice and put up the items I wanted to sell for a 10-day auction, starting on a Thursday. This way buyers had two weekends to bid.

     The big things in life: It's easy to post a small item, but furniture is a big part of eBay and this has to

be collected or sent by delivery men. Check the ways of delivery before you bid.

1. What is the passage mainly about?

A. How to make payment online.

B. Ways of using delivery online.

C. Advantages of an online-auction system.

D. How to use an online-auction system.

2. After bidding for an item, a buyer __________.

A. will get what he wants in ten days

B. should make payment immediately

C. has chances to make higher bids

D. may check its picture and description

3. The easiest way of making payment mentioned in the passage is __________.

A. through an online payment system

B. through a local banking system

C. by sending the money to the seller

D. by paying the deliveryman directly