如图所示装置是模拟膈肌运动的示意图，箭头代表运动方向，请回答下列问题

若单项式2x²y^a+b与$-\frac{1}{3}$x^a﹣by⁴是同类项，则a，b的值分别为（　　）

读拼音，写词语。

根据文章内容和括号内所给汉语的意思，写出各单词的正确形式（每空一词）。

Dear Dad,

    Father's Day is coming. Although I am ____（忙）getting ready for the high school entrance exams, I want to celebrate it for you because you are my ____（英雄）. I'd say, “I love you, Dad!”

    I do think you are the most ____（耐心）father in the world. Every time I have trouble, you always give me advice and help me out. I remember ____（一次）I failed in a competition, I felt terrible. Instead of complaining, you just said to me quietly, “A real man must learn to____（面对）many failures in life bravely. Cheer up!” I repeated your words many times and finally knew what ____（它的）meaning was.

    Dad, I am going to buy you a ____（明信片）as a present. I hope you will like it although I don't think it can ____（表达）all of my thanks to you. I believe you can ____（理解）me. Love you forever, Dad!

Best ____（祝愿）!

Yours,

Mike

如图（a）所示,在光滑水平面上用恒力F拉质量为1kg的单匝均匀正方形铜线框,在1位置以速度v₀=3m/s进入匀强磁场时开始计时t=0,此时线框中感应电动势为1 V,在t=3s时刻线框到达2位置开始离开匀强磁场．此过程中v t图象如图（b）所示,那么（  ）