Many pet owners see their pets as family members. However，when they have to go away on business or for some other reasons，and cannot take their pets along，they feel guilty about it and wish they could do something for their deeply loved pets. The Pet Hotel is set up especially for this reason.

    What do we offer?

    The Pet Hotel offers pets large rooms and the latest equipment（设备）.Like other hotel rooms，we offer color TVs，suitable beds，sofas and other pieces of furniture for pets.

    We prepare great food for the little guests，walk them at least twice a day，and provide them with all kinds of amusements（娱乐活动）. In addition，we brush and clean pets. To make pets feel at home，we play the sort of music which is often played at their homes and turn the TV to the pets' favorite channels. Pets will surely feel comfortable in our hotel!

    We also have video cameras in each room so that owners can check online twenty-four hours a day to make sure that the pets are having a good time at the hotel. We also have phones so that pet owners can call their pets and talk to them every day.

    How much does it cost?

    The prices change according to the size of the rooms. A regular room with standard service costs 1,500 dollars.

如图，双曲线y=$\frac{k}{x}$与y=﹣$\frac{3}{x}$分别为一第一、第四象限，A是y轴上任意一点，B是y=﹣$\frac{3}{x}$上的点，C是y=$\frac{k}{x}$上的点，线段BC⊥x轴于点D，且4BD=3CD，则下列说法：①双曲线y=$\frac{k}{x}$在每个象限内，y随x的增大而减小；②若点B的横坐标为3，则点C的坐标为（3，﹣$\frac{4}{3}$）；③△ABC的面积为定值7，正确的有（　　）

毛皮摩擦过橡胶棒后，橡胶棒带____电．自然界存在____种电荷，它们之 间相互作用的规律是：____．