A、24 hours. B、24 days. C、Three days. D、Three months. D短文开如部分提到，《老大哥》是个非常受欢迎的真人秀节目之一。在节目中，一群陌生人将住进一间屋子里长达三个月，他们的一举一动都将被记录下来。

Almost anything can be the topic of a reality show.(18)"Big Brother" is one of the most popular reality shows, in which a group of people, moved into a house together and were filmed 24 hours a day for three months. These people, who are all strangers, live together, eat together, and share bedrooms. They are isolated from the outside world, while people at home watch them all on TV.(19)The show started in Netherlands in 1999. Soon other countries started their own versions of "Big Brother," and the show became popular all over the world. Another popular reality show is called "Survivor."(20)The idea came from a TV show made in Sweden in 1997. The show leaves a group of ordinary people in a place far away, such as an island or a desert. The people have to find their own food, make fire to keep themselves warm, build their own places to sleep, and participate in difficult challenges. Each week, the participants choose one person to leave the show. The last person left is the winner and wins one million dollars. Today, people in over 20 countries around the world watch to see who will be the survivor!
18. How long do the volunteers in "Big Brother" stay together?
19. When did "Big Brother" start?
20. What does the idea for "Survivor" come from?