Scientists say life will be very different in 2050.

    First，there will be no TV channels（频道）in 2050.People will choose a program from a computer and watch it on TV.In 2050，we will get information from the computers only.

    Second，water will be a big problem in 2050.In many places，people won't have water to drink.

    Third，cars will use new and clean fuels and they will go very fast.There will be a computer in every car.And the computers will control the cars and there won't be any accidents（事故）.

下列哪一个国家最终灭掉了延续千年的拜占廷帝国（    ）

某小型水电站的电能输送示意图如图所示，发电机通过升压变压器T₁和降压变压器T₂向用户供电。已知输电线的总电阻为R=10Ω，降压变压器T₂原、副线圈匝数之比为4∶1，降压变压器副线圈两端交变电压u＝220 sin100πt V，降压变压器的副线圈与滑动变阻器组成闭合电路。若将变压器视为理想变压器，当负载R₀=11Ω时

蜂蜜总含糖量达65％-75％，还含有丰富的酶类，水溶性维生素及钙、铁、锌等。则（）