[originaltext] One of the most commonly-held beliefs of health and nutrition

One of the most commonly-held beliefs of health and nutrition in the UK has been found to be untrue, according to a new scientific study.(16)For many years British people have been recommended to eat at least "five-a-day"—that is five items of fruit or vegetables every day in order to reduce the likelihood of illness, in particular, cancer.(17)The advice was first put forward in 1990 by the World Health Organization which said that the " five-a-day" diet could prevent cancer and other diseases. Many health campaigns have promoted the advice, and indeed much food packaging in Britain states how the contents will constitute part of your five-a-day. However, a study of 500 000 Europeans from ten different countries refutes the commonly-believed suggestion that up to 50% of cancers could be prevented by increasing the public’s consumption of fruit and vegetables. A study led by researchers from a well-respected institute estimates that only 2.5% of cancers could be avoided by eating more fruit and vegetables.(18)It seems that the key to avoiding cancers is to have an overall healthy lifestyle. It includes not smoking or drinking a lot of alcohol, taking exercise and avoiding obesity. But medical institutions have spoken out to remind people that diet is an important factor in staying healthy, and that even a 2. 5% reduction in cancers is still a positive step. Cancer Research UK said that it’s still a good idea to eat your five-a-day but remember that fruit and vegetables are pieces in the whole lifestyle.
16. Which of the following is the commonly-held belief in the UK?
17. Why did British people begin to eat at least "five-a-day"?
18. What is the key measure to avoid cancer according to the passage?