解答题：已知函数f（x）=x2-mx-lnx，m∈R （1）若m=2，求函数f（x）的单

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Science can't explain the power of pets, but many studies have shown that the company of pets can help lower blood pressure (血压) and raise chances of recovering from a heart attack, reduce loneliness and spread all-round good cheer.

Any owner will tall you how much joy a pet brings. For some, an animal provides more comfort than a husband/wife. A 2002 study by Karen Allen of the State University of New York measured stress (紧张) levels and blood pressure in people - half of them pet owners –while they performed 5 minutes of mental arithmetic (算术) or held a hand in ice water. Subjects completed the tasks alone, with a husband/wife, a close friend or with a pet. People with pets did it best. Those tested with their animal friends had smaller change in blood pressure and returned most quickly to baseline heart rates. With pets in the room, people also made fewer math mistakes than when doing in front of other companions. It seems people feel more relaxed (放松)around pets, says Allen, who thinks it may be because pets don't judge.

A study reported last fall suggests that having a pet dog not only raises your spirits but may also have an effect on your eating habits. Researchers at Northwestern Memorial Hospital spent a year studying 36 fat people and their equally fat dogs on diet-and-exercise programs; a separate group of 56 people without pets were put on a diet program. On average, people lost about I1 pounds, or 5% of their body weight. Their dogs did even better, losing an average of 12 pounds, more than 15% of their body weight. Dog owners didn't lose any more weight than those without dogs but, say researchers, got more exercise overall-mostly with their dogs - and found it worth doing.

1．What does the text mainly discuss?

A．What pets bring to their owners.

B．How pets help people calm down.

C．People's opinions of keeping pets.

D．Pet's value in medical research.

2．We learn from the text that a person with heart disease has a better chance of getting well if

A．he has a pet companion

B．he has less stress of work

C．he often does mental arithmetic

D．he is taken care of by his family

3．According to Allen, why did the people do better with pets around when facing stressful tasks?

A．They have lower blood pressure.

B．They become more patient.

C．They are less nervous.

D．They are in higher spirits.

4．The research mentioned in the last paragraph reports that

A．people with dogs did more exercise

B．dogs lost the same weight as people did

C．dogs liked exercise much more than people did

D．people without dogs found the program unhelpful

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已知函数f（x）=x2-mx-lnx，m∈R （1）若m=2，求函数f（x）的单

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