任务型阅读。

     I've got some information for everyone going to Britain next month．As you know,you'll be staying with a family

for two weeks．Now the most important thing is money．You should take about￡30 in cash(现金)and about￡200

in traveler cheques(支票)．Then when you arrive at the airport you'll be met by our host(主人)family．You must

remember to wear a red shirt so the family will find you easily．I've told them to look out for the red shirts．You'll

also need to take with you 4 photos of yourself and,of course,  it's very   important that you take the school letter．

While you are there,if you have any prob1ems,you can call our agent(代理人)．I'll give you her office phone number

now:It's 5804436 and the person to ask for is Mrs．Belcher,that's B-E-L-C-H-E-R．She's in the office from 9-5 every

day．OK! That's everything．Have a good trip．

根据短文内容填写下表,每空词数不限:

与永磁体相比，电磁铁具有以下几个优点：

（1）电磁铁磁性的有无，可以由 _________ 来控制．

（2）电磁铁磁性的强弱可以由 _________ 来改变．

（3）电磁铁的N、S极是由 _________ 来决定．