题目

老鼠的皮毛黄色（A）对灰色（a）为显性。有一位遗传学家，在实验中发现含显性基因（A）的精子和显性基因（A）的卵细胞不能结合。如果杂合的黄鼠与黄鼠（第一代）交配得到第二代，后代（第二代）相同基因型老鼠继续交配一次得到第三代，那么在第三代中黄鼠的比例为（假定每对老鼠产生的后代数量相同）：   A．40％            B．44．4％           C．66．7％           D．75％ Less TV Reduce Kids Weight 　　PALO AITO, California－“ Switching off the television may help prevent children from getting fatter－even if they do not change their diet or increase the amount they exercise,” US researchers said last week． 　　A study of 192 third and fourth grades, generally aged eight and nine, found that children who cut the number of hours spent watching television gained nearly two pounds(0.91 kg)less over a one-year period than those who did not change their television diet． 　　“The findings are important because they show that weight loss can only be the result of a reduction in television viewing and not any other activity,” said Thomas Robinson, a pediatrician(儿科专家)at Stanford University． 　　“ American children spend an average of more than four hours per day watching television and videos or playing games, and rates of childhood being very fat have doubt over the past 20 years,” Robinson said． 　　In the study, presented this week to the Pediatric Academic Societies’ annual meeting in San Francisco, the researchers persuaded about 100 of the students to reduce their television viewing by one-quarter to one-third． 　　Children watching fewer hours of television showed a significantly smaller increase in waist size and had less body fat than other students who continue their normal television viewing, even though neither group ate a special diet nor took part in any extra exercise． 　　“One explanation for the weight loss could be the children unstuck to the television may simply have been moving around and burning off calories,” Robinson said． 　　“Another reason might be due to eating fewer meals in front of the television．Some studies have suggested that eating in front of the TV encourages people to eat more,” Robinson added． (1) The author tries to tell us in the first two paragraphs that ________． [　　] A． children will get fatter if they eat too much． B． children will get thinner if they eat less． C． children will get fatter if they spend less time watching TV． D． children will get fatter if they spend more time watching TV． (2) According to the passage, the time American children usually spend on watching TV ________． [　　] A． is more than four hours a day． B． is less than four hours a day． C． doubled in the last twenty years． D． is more than on any other activities． (3) The time children spend on TV viewing every day is suggested to be about ________． [　　] A． six hours B． eight hours C． three hours D． one hour (4) Which of the following is right? [　　] A． Children usually eat fewer while watching TV． B． Children usually eat more while watching TV． C． Children eat the same amount of meals while watching TV． D． Children usually eat nothing while watching TV． (5) Why can watching TV increase kids’ weight according to the passage? [　　] A． They usually eat more while watching TV． B． They burn off fewer calories． C． They change their diet while watching TV． D． Both A and B