Questions 26 to 28 are based on the passage you have just heard。
26. What is the main topic of the passage?
27. Why dont all ice crystals in clouds immediately fall to Earth?
28. In this passage, what does the term coalescence refer to?
Passage Two
Good locks on all outside doors and first floor windows are essential to a homes security and will go a long way towards discouraging burglars. But an added protective device that is increasingly being used in homes is the burglar alarm system, which sounds a loud bell when someone tries to break in. Although this will not always prevent entry by a professional burglar, it is often enough to scare off thieves who account for a high percentage of residential break-ins。
Security alarm systems have all been available for many years and have long been common in commercial and industrial establishments and in large homes. But until the last few years, these system were almost always professionally installed because they required complicated wiring techniques, individualized design and sometimes lots of carpentry---all of which made them expensive。
To answer the demand for low-cost alarm systems that can be easily installed, several companies now make alarms that are specifically designed as do-it-yourself。 These systems come with detailed installation instructions and usually do not require inside-the-wall-wiring。
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