A、The windows. B、The front door. C、The living room. D、The back door. A文章在开头部分提到，在所有房屋中最不安全的地方就是小偷们经常进入的地方，也就是窗户，故答案为A)。

Home security, of course, refers to making sure that no one can enter your home without your permission. I’ve put together a list of do’s and don’ts that you should follow.
     (20)The least secure point in any home, and the place that thieves most often use to gain entry to your home, is the windows. Therefore, make sure you fit secure locks to all the windows in your home. And don’t forget the small ones either.
    Now the main point of entry into any home is, of course, the front door.(21)Therefore, a good, sturdy wooden door is essential, as well as a good quality lock that can be locked from the outside by the means of a key. But avoid doors with glass in them. Glass can easily be broken allowing a burglar access to the main lock. And a good quality burglar alarm is also a good investment.
    Of course, most people generally take a holiday once a year. Therefore, when you do go away for any length of time, even if it’s only for a few days, there are certain precautions that you should take. For instance, if you have a newspaper delivered in the morning make sure(22)you cancel the delivery for the time that you are away. And the same for other items such as milk and bread. Also contact the post office. Tell them that you will be away and ask them to leave your mail with a neighbor. But do ask your neighbor’s permission first!
20. What is the least secure point in the house?
21. What is essential to prevent others entering your house without your permission?
22. What precautions should we take before going on holiday?