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有甲、乙两种糖，因售货员工作不慎，误把两种糖混倒在一起，已知甲种糖10kg，单价5.70元，乙种糖20kg，单价6元，若将这两种糖混合均匀后出售，应把单价定为[ ]

A．6.00元

B．5.90元

C．5.80元

D．5.70元

答案

答案：B

填空题

Small dogs generally live longer than big dogs so that yappy Yorkshire terrier next door could be around for a long time. But body size isn’t the only factor that (36) how long dogs survive. Personality influences life span, too, according to a new study that might help explain how animal (37) evolve.
Research on animals from ants to apes has found that different (38) have different personalities. Some are timid, others (39) . Biologists have proposed that temperaments evolved along with life history. (40) , violent animals use a lot of energy fast in (41) short lives, the thinking goes, whereas calmer animals last longer, saving themselves to (42) later in life.
But it’s hard to run evolutionary (43) on these personalities in anything longer lived than a fruit fly. So evolutionary biologist Vincent Careau of Universit6 de Sherbrooke in Canada came up with an idea: dogs. "All these breed differences reflect an experiment on artificial selection," says Careau. (44) , but from generations of humans crossbreeding and selecting animals with traits---the ability to chase foxes into holes, or herd sheep, or sit attractively on a sofa.
But evolutionary physiologist Joseph Williams of Ohio State University in Columbus isn’t convinced that (45) . "For me, it still remains to be seen. Dogs are contrary to what you would expect in nature in terms of longevity," he says. Elephants live for decades, (46) . On the other hand, a Chihuahua will generally outlast a Saint Bernard.
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判断题

开坡口的目的主要是保证焊件在厚度方向上全部焊透。
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