A、To compare clocks to human beings. B、To tell readers what clocks look like. C、To describe why clocks can rule the planet Earth

How should one invest a sum of money in these days of inflation? Left in a bank it will hardly keep its value, however high the interest rate. Only a brave man, or a very rich one, dares to buy and sell on the Stock Market. Today it seems that one of the best ways to protect your savings, and even increase your wealth is to buy beautiful objects from the past. Here I am going to offer some advice on collecting antique clocks, which I personally consider are among the most interesting of antiques.
    I sometimes wonder what a being from another planet might report back about our ways of life. "The planet Earth is ruled by a mysterious creature that sits or stands in a room and makes a strange ticking sound. It has a face with twelve black marks and two hands. Men can do nothing without its permission, and it fastens its young round people’s wrists so that everywhere men go they are still under its control. This creature is the real master of Earth and men are its slaves."
    Whether or not we are slaves of time today depends on our culture and personality, but it is believed that many years ago Kings kept special slaves to tell the time. Certain men were very clever at measuring the time of day according to the beating of their own hearts. They were made to stand in a fixed place and every hour or so would shout the time. So it seems that the first clocks were human beings.
    However, men quickly found more convenient and reliable ways of telling the time. They learned to use the shadows cast by the sun. They marked the hours on candles, used sand in hour-glasses, and invented water-clocks. Indeed, any serious student of antiques should spend as much time as possible visiting palaces, stately homes and museums to see some of the finest examples of clocks from the past.
Questions 19 to 21 are based on the passage you have just heard.
19. What do we know about collecting antique clocks according to the speaker?
20. What does the speaker intend to do by quoting the remark of a being from another planet?
21. What is the purpose of the talk?