A、It was difficult to produce the dye in the past. B、It is the choice of many chocolate companies. C、It was the colour used by r

Take five colours: red, black, blue, green and purple. How do they make you feel?
    Red is, of course, considered fortunate in China. (22) Studies have indicated that red "raises blood pressure," and claim that it stands out from other colours. Hemingway says it appears to be "coming towards you," and so is useful for emergency and alarm signs, and also for conveying "urgency" in general.
    Black has a different sense. In the West, it’s associated with death, but that hasn’t stopped it becoming a mysterious colour. Hemingway says it’s the colour of luxury brands: things like "designer watches" are often black.
    Blue, by contrast, is cool and peaceful. The colour is a constant presence in our lives, says Hemingway, being the colour of the sky and the sea. (23) That gives it an air of being reliable, which makes it a firm choice with "banks and corporations." Hemingway says this is also why emergency services often choose the colour.
    Green is, unsurprisingly, the colour of nature and the environment. (24) Giving a product green packaging creates the impression it is environmentally friendly. Hemingway also says that green is the colour of growth and movement; it’s used to indicate "go" on traffic lights.
    Finally, we have purple, which is associated with valuable things. (25) In the past, purple dye was expensive because it was very difficult to produce, and it became the colour worn by royalty in many Western countries. These days, companies still use purple to make their product seem more exclusive, whether they’re selling chocolate or cigarettes.
Questions 22 to 25 are based on the passage you have just heard.
22. What is the feature of red according to studies?
23. Why do banks and corporations tend to choose blue?
24. What is the reason for green to be used for packaging?
25. What makes purple associated with valuable things?