A、A heater is not needed at all. B、Devices can be used for free. C、It is as basic as possible. D、It can be freely moved. D录音提到移动

A mobile office is, quite literally, an office which is capable of mobility. This means that wherever in the country that office is needed, it can be relocated to. Mobile offices are commonly used by salespeople who have to work out of their normal company offices. As salespeople often travel the length and breadth of the country looking for people who are interested in what they are selling, they often need someplace to set up a temporary office as they may spend a long period of time in one place. It is then easy for salespeople or people with a similar occupation who are working away from their main offices to connect with their company via the portable computers, such as laptops and mobile phones. It is for this reason also that a mobile office is ideal—the office can be transported from one location to another with relative ease. The staff who are currently employed within the temporary office then do not have to put in much effort to making the temporary office functional and efficient for the job that they need to do and work can often be started almost immediately.
    There are many advantages to renting a mobile office. For example, this office is a lot cheaper than renting a hall or a building for temporary office work. If one were to rent an already standing building, such things as heating and flowing water may have to be paid for on top of the rent. With a mobile office, one does not have to pay for heating but may instead use a portable heater that runs off mains electricity. Mobile offices can be connected to mains electricity or can be connected to a generator which provides electricity to the portable office. This allows people working within a mobile office to use devices such as laptops, printers and photocopiers and a kettle freely. A portable office is not as basic as some may believe—it may be described as a continuation of a main office. A portable office may also be specifically designed to meet an office need. A hired building may not have everything needed to convert it into a fully functioning and effective office environment. After a mobile office has been converted into a functioning office, it can be freely moved around the country to suit the needs of whoever is using it.
    There are many companies these days that specialise in mobile offices, so finding one to provide a mobile office is not difficult. Many companies can provide a mobile office tailored to the type of work that needs to be done.
19. Why do salespeople need a mobile office?
20. What is the advantage of mobile offices?
21. What do we learn about mobile offices?