在工业锅炉对湿度的要求中，水管锅炉的湿度应控制在（）以下。A、15% B、10% C

Hello, boys and girls. My name is Wu Da. It’s Sunday, 小题1:__________we are all in the 小题2:________. Look! Our English teacher is talking with some 小题3:__________. What are we doing? We are having a(n) 小题4:___________ in the classroom. Now, Li Ming is singing an English song.小题5:_________ is playing the piano? Oh, it’s Xia Xue. She has two piano lessons every 小题6:__________, and she can play the piano very 小题7:________. Wang Hao and Hu Min are dancing to the music.

Who is the little boy? That’s Guo Kai, our English teacher’s 小题8:_________. He is only four years old. He is eating a(n) 小题9:__________. Why are we having the party? Today is Steve’s 小题10:___________. His parents are working in another city and can’t have a birthday party for him. So we have it for him. Steve is really happy.

质量为m=3kg的木块，放在水平地面上，木块与地面的动摩擦因数μ=0.5，现对木块施加F=30N，方向与水平方向成θ=370的拉力，如图所示，木块运动4s后撤去拉力F直到木块停止．（sin37°=0.6，cos37°=0.8，g=10m/s²）求

（1）撤去拉力F时木块的速度为多大；

（2）木块在水平面上运动的位移为多少．

设f₀（x）=sinx，f₁（x）=f₀′（x），f₂（x）=f₁′（x），…，f_n+1（x）=f_n′（x），n∈N，则f₂₀₁₁（x）=（　　）

A．-cosx

B．cosx

C．-sinx

D．sinx

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