（2015•涿州市校级模拟）环境对人种的形成有较大影响．一般说来，黑人多分布在（  ）

阅读下面的诗，回答相关问题。

                                                                           麦陇风来翠浪斜，

                                                                           草根肥水噪新蛙。

                                                                           羡他无事双蝴蝶，

                                                                           烂醉东风野草花。

小明同学利用如图甲所示的电路探究电流跟电阻的关系．已知电源电压为6V且保持不变，实验用到的电阻阻值分别为5Ω，10Ω，15Ω，20Ω，25Ω

已知 $\{\begin{array}{c}x=2\\ y=1\end{array}$ 是二元一次方程组 $\{\begin{array}{c}ax+by=7\\ ax-by=1\end{array}$ 的解，则 $a-b$ 的值为（      ）

阅读下列短文，从每题所给的A、B、C、D四个选项中选出最佳选项。
A
Live Music—-Late Night Jazz
    Enjoy real American jazz from Herbie Davis, the famous trumpet(号手). He is known to play well into the early hours, so don't want to get much sleep.

PLACE: The Jazz Club     DATES: 15—-23 June PRICE: ￥100-150        TIME: 10 p.m. till late!   TEL: 4668736

Scottish Dancing
    Scottish dancing is nice and easy to learn. The wonderful dance from England will be given.

PLACE: Jack Stein's      DATES: 10-20 May PRICE: ￥150           TIME: 7-10 p.m.  TEL: 4021877

Shows—-Anhui Museum
    There are 12,000 pieces on show here. You can see the whole of Chinese history.

PLACE: Anhui Museum    DATES: 1Mar-30 Jun PRICE: ￥130            TIME: Mon-Fri 9 a.m-5 p.m.   Saturday 9 a.m.-9 p.m. TEL: 4886888

    Your pen friend is coming from Australia to your city for a holiday. You send him this E-mail to tell him something about the hotels.

SUN HOTEL Dates                Prices(a night) 1Oct-31Dec             ￥168 1Jan-31Mar             ￥148 1Apr-30Apr(closed)       …… 1May-31May            ￥188 1Jun-30Sep              ￥208 TEL: 4686788   E-mail: Li Hong@163.com.

ROSE HOTEL Prices(a night) ￥198 ￥178 …… ￥218 ￥248