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Kids love to go online. There is so much to explore and learn. 小题1: The answer to the question is as difficult as determining at what age a child can be left at home by themselves, since all children are different. Here are some questions to ask yourself to determine what is right for your child. 小题2: Of course when you are trying to determine if your can let him or her go online, your child has probably already said, “I’m ready;I can handle it”. But are they? _____ 小题3: _____ How would they handle the material if they ran across it by accident? 小题4: Does your child question other people’s actions? Do they easily believe anything that is presented to them? It is an important question to ask to determine if your child is ready to go online alone. Have you taught them what the dangers are? 小题5: Have you explained to them that there are people out there that might want to do them harm? It is a dangerous world out there. If you are going to let them wander around in the online world, they need to be prepared for what they might see or run into. A.Is your child easy to cheat? B.There are a lot of dangers online. C.Are they ready to go online by themselves? D.Is your child skilled in using a computer? E. Unfortunately there is a lot of unpleasant material online. F. At what age should you allow your child to go online alone? G. You may be thinking this is a strange question to ask yourself.
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【简答题】麻黄发汗、解热、抗炎的药理作用与其 功效相关。
【单选题】到 (-3,0) , (3,0) 距离之差的绝对值等于 6 的点的轨迹
A.
椭圆
B.
双曲线
C.
双曲线一叶
D.
两条射线
【单选题】下列关于限制酶反应的说法错误的是
A.
限制酶识别序列内或其邻近的胞嘧啶、腺嘌呤或尿嘧啶被甲基化后,可能会阻碍限制酶的酶解活性。
B.
许多限制酶对线性DNA和超螺旋DNA底物的切割活性是有明显差异的。
C.
有些限制酶对同一DNA底物上不同酶切位点的切割速率会有差异。
D.
限制酶反应缓冲系统一般不用磷酸缓冲液,是由于磷酸根会抑制限制酶反应。
E.
BSA对许多限制酶的切割活性都有促进作用,所以酶切反应中常加入一定量的BSA。
【多选题】卤代烷与氢氧化钠的水 - 醇溶液中进行反应,下列现象属于 S N 1 机理的有 ( )
A.
产物外消旋化
B.
叔卤代烷反应速率明显大于仲卤代烷的反应速率
C.
产物构型完全转化
D.
有重排产物
【单选题】到 (-3,0) , (3,0) 距离之差等于 5 的点的轨迹
A.
B.
椭圆
C.
双曲线
D.
双曲线一叶
【单选题】到 (-3,0), (3,0) 距离之差的绝对值等于 4 的点的轨迹
A.
B.
椭圆
C.
双曲线
D.
双曲线一叶
【多选题】卤代烷与氢氧化钠的水-醇溶液中进行反应,下列现象属于SN1机理的有:
A.
产物构型完全转化
B.
叔卤代烷反应速率明显大于仲卤代烷的反应速率
C.
有重排产物
D.
产物外消旋化
【单选题】设动点M到A(-5,0)的距离与它到B(5,0)的距离之差等于6,则P点的轨迹方程是(    )
A.
='1'
B.
=1
C.
=1(x≤-3)
D.
=1(x≥3)
【单选题】下列关于限制酶反应的说法错误的是?
A.
限制酶识别序列内或其邻近的胞嘧啶、腺嘌呤或胞嘧啶等被甲基化后,可能会阻碍限制酶的酶解活性
B.
许多限制酶对线性DNA和超螺旋DNA底物的切割活性是有明显差异的
C.
BSA对许多限制酶切割活性有促进作用,所以酶切反应中常加入一定量的BSA
D.
限制酶反应缓冲系统一般不用磷酸缓冲液,是由于磷酸根会抑制限制酶反应
【多选题】卤代烷与氢氧化钠的水 - 醇溶液中进行反应,下列现象属于 SN1 机理的有:
A.
产物外消旋化
B.
增加氢氧化钠浓度,反应速度明显加快
C.
有重排产物
D.
叔卤代烷反应速率明显大于仲卤代烷的反应速率
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