Computers are now as commonly used in business as the telephone. Therefore, it's important that people know how to use (21) efficiently. Now, you and your whole organization are able to do this in the simplest way possibly (22) learning and pract

Computers are now as commonly used in business as the telephone. Therefore, it's important that people know how to use (21) efficiently. Now, you and your whole organization are able to do this in the simplest way possibly (22) learning and practicing on your own, with (23) wide range of courses at beginning, intermediate and advanced level on CD-ROM.
The person (24) appears on the screen acts your teacher, (25) you through the tasks and explaining everything. Then (26) difficult exercises allow you to practice the things you (27) learned and test your understanding.
(28) courses are excellent bargain only $69. 99. You (29) save yourself money if you buy a complete collection of courses. This is available (30) the retail price of $410. You need to hurry up as there is a great demand at the moment.
回答第（30）空

A.over

B.at

C.from

正确答案是B