Good morning, class. Today’s topic is "Idioms and Their Origins". An idiom is a phrase or expression with【C1】______. The meaning of an idiom often cannot be understood from the meaning of【C2】______in it. In our language, idioms are an important part and they often make our language【C3】______. So in today’s lecture, let’s look at the origins of some English idioms. The first【C4】______on our list is "Raining cats and dogs". This is an interesting phrase. It is【C5】______the well-known antipathy between dogs and cats, which is【C6】______in the phrase "fight like cat and dog". However, there are【C7】______about the origin of the well-known expression, "Raining cats and dogs". One theory is that【C8】______, the roofs on houses were made of hay. You’ve probably heard of【C9】______, well that’s all they were. Thick straw, piled high, with【C10】______. Those thatch roofs were the only place for the little animals to【C11】______. So all the pets in the house; dogs, cats and【C12】______, even mice, rats, bugs, all lived in the roof. When it rained 【C13】______so sometimes the animals would slip and 【C14】______. Thus the saying, "it’s raining cats and dogs. " Another explanation is that heavy rain would wash dead animals【C15】______. In the 18th century, streets in England were rather filthy and heavy rain would occasionally 【C16】______dead animals and other debris. The animals didn’t fall from the sky, but the sight of dead cats and dogs 【C17】______in storms could well have caused the coining of this colourful phrase. The most popular one comes from 【C18】______in which cats were a symbol for rain and dogs 【C19】______. Thus, "it’s cats and dogs out there" is often used to describe 【C20】______with strong winds.【C19】