如图所示是一按正弦规律变化的交流电的u﹣t图．关于此交流电的下列结论正确的是（   ）

如图所示，放在水平桌面上的木块A处于静止状态，所挂的砝码和托盘的总质量为0.6kg，弹簧测力计读数为2N，滑轮摩擦不计．若轻轻取走盘中的部分砝码，使总质量减少到0.3kg，将会出现的情况是（g=10m/s²）（   ）

    Some years ago,writing in my diary used to be____usual activity. I would return from school and spend half an hour ____(record)the day's events, feelings, and ____(impress)in my little blue diary. I did not really need ____(express) my emotions by way of words, but I gained a certain satisfaction from ____(see) my experiences forever recorded on paper, After all, isn't accumulating(积累）memories a way of preserving the past?

    ____ I was thirteen years old, I went on a long journey____ foot in a great valley____(equip) with pens, a diary, and a camera. During the trip, I was busy recording every incident, name and place I came across. I felt ____(pride) to be spending my time productively, dutifully preserving for future generations a detailed description of my travels. On my last night there, I ____(walk)out of my tent, diary in hand.

某化学小组同学从微观角度进一步理解复分解反应的实质．

（1）复分解反应的实质是某些阴、阳离子结合生成沉淀、气体或____的过程．
（2）根据复分解反应的实质，形成一个复分解反应网络图（如图所示，图中直线相连的阴、阳离子之间能够两两结合发生反应），请选择合适的离子填入如图括号内（____，____），使其两两结合时，一个有气体产生，一个有沉淀（注：沉淀与珍珠粉的成分相同）生成，其中有气体生成的化学反应方程式可能是____．