单项选择题
核酸的理化性质及其应用：下列关于核酸的解离性质描述正确的是（）。
A、核酸分子中有很多磷酸基团，在溶液pH大于其等电点时呈酸式解离，形成多价阴离子
B、核酸分子中有很多磷酸基团，在溶液pH大于其等电点时呈碱式解离，形成多价阴离子
C、核酸分子中有很多可呈碱式解离的磷酸残基和可呈酸式解离的氮原子，因此核酸属于两性化合物
D、DNA双螺旋两条链间氢键的形成与其解离状态有关，在pH4.0~11.0范围内碱基最为稳定
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未知题型
Some pessimistic experts fleel that the automobile is bound to fall into disusE.They see a day in the not-too-distant future when all autos will be abandoned and allowed to rust. Other authorities, however, think the auto is here to stay. They hold that the car will remain a leading means of urban travel in the foreseeable futurE.The motorcar will undoubtedly change significantly over the next 30 years. It should become smaller, safer, and more economical, and should not be powered by the gasoline enginE.The car of the futtire should be far more pollution-free than present types.Regardless of its power source, the auto in the future will still be the main problem in urban traffic congestion(拥挤). One proposed solution to this problem is the automated highway system.When the auto enters the highway system, a retractable(可伸缩的) arm will drop from the auto and make contact with a rail, which is similar to those powering subway trains electrically. Once attached to the rail, the car will become electrically powered from the system, and control of the vehicle will pass to a central computer.The computer will then mortitor all of the car's movements.The drivet will use a telephone to dial instructions about his destination into the system. The computer will calculate the best route, and reserve space for the car all the way to the correct exit from the highway. The driver will then be free to relax and wait for the buzzer(蜂鸣器) that will warn him of his coming exit. It is estimated that an automated highway will be able to handle 10,000 vehicles per hour, compared with the 1,500 to 2,000 vehicles that call be carried by a present-day highway.One significant improvement in the future car will probably be______.A.its power sourceB.its driving systemC.its mollitoring systemD.its seating capacity
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单项选择题
会议的议题是根据会议目标确定并付诸会议讨论或解决的具体问题，是会议活动的必备要素。
A.正确
B.错误 -
未知题型
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A.following
I.coming
J.according
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