一匹雄性黑马与若干匹纯种枣红马交配后，共生出20匹枣红马和23匹黑马。下列叙述中最可能的是（  ）
①雄性黑马是杂合体  ②黑色是隐性性状
③枣红色是显性性状  ④枣红色是隐性性状

1917年11月7日晚，“阿芙乐尔”号巡洋舰发出向敌人最后攻击的炮声，赤卫队员、革命士兵和水兵的队伍从四面八方冲向冬宫。随后，世界上第一个社会主义国家诞生。这一事件是（    ）

男孩和女孩在做同一件事的时候，别人对我们的____和____会不一样。

B

    As we all know，having a great memory is important．It can help you succeed in school，in your job，and in life．It also helps you learn faster and better．We all know that fast learner's are always in demand．If you have a great memory, I'm sure you can succeed more easily．

    If you are willing to make a few changes in your life．you should improve your memory first．My plan is to explain every skill that can help you improve your memory．

    You can not only learn memory skills on this website，but also learn how to improve your memory through diet，exercise，sleep and other ways．

    I think that memory improvement can be achieved (实现)in two ways：improving the health of your brain and using memory skills．Many people think they may be difficult．In fact, they are easier to do than you might think，but you have to work hard by yourself.

    Memory improvement needs time and effort on your part．You cannot improve your memory if you do not work on it．Of course，I believe that a more powerful brain is well worth the effort!

    Here are a few of the great memory improvement tips．I will give you some tips in the following part．

一理想变压器的原线圈连接一只电流表，副线圈接入电路的匝数可以通过滑动触头Q调节，如图所示，在副线圈上连接了定值电阻R₀和滑动变阻器R，P为滑动变阻器的滑动触头，在原线圈上加一电压为U的正弦交变电压，则（   ）