下列划线的字注音有错误的一组是( )。
A:搓捻(cuō niǎn) 绽开(zhàn) 怦怦直跳 (pēng)
B:小憩(qì) 繁衍(yǎn) 恍然大悟(huǎng)
C:遨游(áo) 觅食(mì) 花团锦簇(cù)
D:迁徙(xǐ) 茁壮(chuó) 冥思遐想(xiá)
①2是函数f(x)的一个周期;
②f(x)的图象关于直线x=2对称;
③f(x)是偶函数;
④(﹣1,0)是函数f(x)的一个对称中心.
其中正确说法的个数为( )
下列事例中,没有利用超声波的是( )
Dear Dad, Happy birthday to you ! On this special day I'd like to talk to you1a special way. I don't think I am good at2you my thought face to face with you,so I'm writing to show my deep love for you.You're not a rich man or a famous person.But in my heart,you are one of the greatest3 in the world.I am4 you. You are5 interested in fame and wealth.You do6 things like paying phone bills on time,and working as a worker in your factory.The smile on your face shows you are pleased with the family.You take good care of my grandparents.You help me with my schoolwork and do some shopping with Mom on Sundays. In the past,I didn't care7 you were with me or not.Now I am sorry to say I8 you the respect before.But I am thankful for what you have done for me. I am quite lucky that I have9 a great father.And I feel happy that now I can let you10 how much I love you.You are successful as a son,a husband,a father,and a friend. Wish you happy forever! Yours,
David
生物实验中常常需要设置对照,以下对照设置正确的是( )
直角三角形有
锐角三角形有
钝角三角形有
等腰三角形有
等边三角形有