题目内容：

Next time you raise an eyebrow at the views of your partner, friend, sibling （兄弟姐妹） or colleague, remember they could be helping to make you smarter. New research shows that intelligence is not fixed but can be improved throughout adulthood by family members, bright mates and intellectually challenging careers. The study challenges the commonly held belief that intelligence is fixed by the age of about 18.

Scientific consensus suggests that intelligence is controlled by genes, with environmental factors such as schooling and nutrition playing a partial role up to this age. After this point, IQ scores become steady（稳定的）. But James Flynn, professor of political studies and psychology at the University of Otago in New Zealand, argues that people can "upgrade" their own intelligence throughout their lives. He believes intellectual stimulation（刺激）from others is important as the "brain seems to be rather like a muscle - the more you use it, the stronger it gets". However, the opposite is also true - so people sharing a home or workplace with those who are intellectually challenged risk seeing their IQ levels nosedive as a result.

Professor Flynn analyzed US intelligence tests from the last 65 years and created new IQ "age tables". He found a bright ten-year-old with brothers and sisters of average intelligence will suffer a five to ten point IQ disadvantage compared to a similar child with equally bright brothers and sisters and special educational treatment to help pull them up.

Professor Flynn also concluded that although genetics and early life experiences determine about 80% of intelligence, the remaining 20% is linked to lifestyle. This means that people can raise their IQ, or allow it to fall, by ten points or more. He suggested the best way to improve IQ levels is to mix with bright friends, find an intellectually challenging job and marry someone cleverer.

1.According to the text, it is commonly believed that ______ .

A. people' s IQ level falls as they age

B. it is wise to share family members' views

C. people cannot improve their intelligence during adulthood

D. doing something challenging is good for one's intelligence

2.The underlined word "nosedive" in paragraph 2 probably means ______ .

A. vary    B. develop

C. change    D. fall

3.Which of the following can help improve one's intelligence according to Professor Flynn？ ______

A. Making many friends.

B. Staying with smart people.

C. Doing exercise every day.

D. Learning from brothers or sisters

4.The purpose of the text is to ______ .

A. inform    B. advertise

C. entertain    D. persuade