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Does your older brother think he’s cleverer than you ? Well, he’s probably right． According to a new research published in the journal Intelligence, the oldest children in families are likely to have the highest IQs and the youngest the lowest ,
A number of studies have suggested that IQ scores decline with birth order． In the most recent study, at Vrije University, Amsterdam,researchers looked at men and women whose IQ had been tested at the ages of 5，12 ，and 18．
The results , which show a trend for the oldest to score better than the youngest in each test, involved about 200,000people． That showed that first-borns had a three-point IQ advantage over the second-born, who was a point ahead of the next in line．
The order of birth can also affect personality, achievement, and career, with first-borns being more academically successful and more likely to win Nobel prizes． However,eldset children are less likely to be radical and pioneering ． Charles Darwin, for example, was the fifth child of six．
Exactly why there should be such differences is not clear, and there are a number of theories on environmental influences on the child．
The so-called dilution(稀释法) theory suggests that as family resources, both emotional and physical, as well as economic, are limited, it follows that, as a result , as more children come along, the levels of parental attention and encouragement will drop． Another theory is that the intellectual(智力) environment in the family favors the first-born who has, at least for some time, the benefit of individual care and help．
The theory which enjoys the most support is that the extra time and patience that the earlier-borns get from their parents, compared with those arriving later, gives them an advantage．
1．What is the passage mainly about?
A．IQ scores have little to do with the order of birth．
B．Intellectual families favor the first-born
C．The order of birth can have an effect on IQ
D．The order of birth can affect personality, achievement, and carrer．
2．By using Charles Darwin as an example, the author wants to prove that         
A．eldest children are the smartest in a family
B．youngest children will usually become experts
C．first-borns are more likely to win Nobel prizes
D．eldest children are less likely to try something new
3．What do we know about the dilution theory?
A．Intellectual parents love the first –born better
B．Parents’ attention will drop with more children coming
C．Family resources,both emotional and physical are endless．
D．First-born get less care and help from their parents．
4．The passage is developed mainly by         
A．offering opinion with further explanation
B．pointing out similarities and difference
C．comparing opinions from different fields
D．providing typical examples