母爱是伟大的！母亲在怀孕期间，身体负担明显加重，母亲和胎儿之间进行物质交换的结构是（ ）
A．胎盘
B．脐带
C．子宫
D．输卵管
胎儿生活在子宫内半透明的羊水中，通过胎盘、脐带与母体进行物质交换．从母体中获得营养物质和氧，胎盘呈扁圆形，是胎儿和母体交换物质的器官．胎盘靠近胎儿的一面附有脐带，脐带与胎儿相连．胎盘靠近母体的一面与母体的子宫内膜相连．胎盘内有许多绒毛，绒毛内有毛细血管，这些毛细血管与脐带内的血管相通，绒毛与绒毛之间则充满了母体的血液，胎儿和母体通过胎盘上的绒毛进行物质交换，而胎儿产生的废物也是经胎盘由母体排出体外的．
故选：A．
Young people are often unhappy when they are with their parents，They 1 that their parents don’t understand them，They often think their parents are too strict with them. Parents often find it difficult to win their children’s trust(信任)and they seem to forget how they themselves 2 when they were young. For example，young people like to do things without much thinking. It’s one of their ways to 3 that they grow up and they can deal with any difficult things. Older people worry more easily. Most of them plan things 4 and don’t like their plans to be changed. Young people often make their parents 5 by clothes they want，the music they enjoy and something else. But they don’t mean to cause(引起)any trouble. They just want to be 6 and they want to make a new culture(文化) of their own. Sometimes you even don’t want your parents to say“ 7 ”to what you do. You want to stay at home and do what you like. If you plan to control（控制） your 8 ，you’d better win your parents over and try to get them to 9 you. If your parents see that you have high sense of responsibility(责任),they will 10 give you the right(权利) to do what you want to do.
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