当皮肤划破时有时会流血，说明皮肤中包含____组织．

如图是先天聋哑遗传病的某家系图，Ⅱ₂的致病基因位于1对染色体，Ⅱ₃和Ⅱ₆的致病基因位于另1对染色体，这2对基因均可单独致病．Ⅱ₂不含Ⅱ₃的致病基因，Ⅱ₃不含Ⅱ₂的致病基因，不考虑基因突变．下列叙述正确的是（  ）

    Every year on April 22, People all over the world celebrate Earth Day. It is a time to work to keep our earth clean. People plan projects to clean up the land, air and water.
    U.S. Senator Gaylord Nelson first thought of the idea for Earth Day in 1962 when he saw polluted rivers and cities with smoke. He needed to get support from Americans to clean up the earth. Finally, on April 22, 1970, 20 million Americans celebrated the first Earth Day! Now many countries around the world celebrate it, and you can, too.
How can you celebrate Earth Day? Here are a few ideas:
Join a clean-up project------Clean up your street or a favorite beach.
Save energy------Turn off the lights when you leave a room, and use public transportation.
Use less water.
Reduce(减少)/ Reuse/ Recycle ------ Practice the three Rs: First, reduce how much you use. Then reuse or recycle what you can.
You can make a difference on Earth Day and every day!

设函数D(x)＝，则下列结论错误的是   （   ）