A、The increasing knowledge about micro-organisms. B、The industrialization of the making process. C、The expansion of the scale of

Hello, everyone. Today we are going to talk about some general knowledge about cheese. Cheese is one of those foods that we tend to take for granted as always having been with us, and it’s strange to think mat someone somewhere must have discovered the process that takes place when micro-organisms get into milk and bring about changes in its physical and biochemical structure. Obviously, we don’t know who discovered the process, but it’s thought that it came from Southwest Asia about 8,000 years ago.
    Early cheese was probably rather tasteless in the case of the so-called " fresh cheeses," which are eaten immediately after the milk has become very thick, or rough tasting and salty in the case of the "ripened cheeses," which are made by adding salt to the soft fresh cheese and allowing other biochemical processes to continue so that a stronger taste and a more solid texture results.
    The ancient Romans changed all that. They were great pioneers in the art of cheese making, and the different varieties of cheeses they invented and the techniques for producing them spread with them to the countries they invaded. The spread of new techniques took place between about 60 BC and 300 AD. You can still trace their influence in the English word " cheese," which comes ultimately from the Latin word "cheese," that’s C-A-S-E-U-S.
    Well, things went on quietly enough after the Roman period with the cheese producers in different countries getting on with developing their own specialties. In the 19th century, with the increasing knowledge about micro-organisms, there came the next great step forward in cheese-making. Once it was known exactly which micro-organisms were involved in the different stages of producing a cheese, and how the presence of different micro-organisms affected the taste, it was possible to introduce them deliberately, and to industrialize the process.
    Cheese started being made on a large scale in factories, although the small producer working from his farm dairy continued to exist and still exists today. Cheese-making moved very much into the world of technology and industrial processes, although, because the aim is still to produce something that people like to eat, there’s still an important role for human judgment. People still go round tasting the young cheese at different stages to see how it’s getting on, and may add a bit of this or that to improve the final taste. Whatever the scale of production, there is still room for art, alongside the technology.
    OK, mat’s all for today’s lecture. Thank you for listening.
    Questions 19 to 22 are based on the recording you have just heard.
    19.What does the speaker say about cheese?
    20. According to the speaker, how was cheese spread to other countries?
    21.What contributed to the great step forward in cheese-making in the 19th century?
    22.What does the speaker say about cheese-making today?