一种测定风作用力的仪器原理如图所示，它的细长金属丝一端固定于悬点O，另一端悬挂着一个质量为m金属球，无风时，金属丝自然下垂，当受到沿水平方向吹来的风时，金属丝将偏离竖直方向角度θ．风力越大，偏角越大，下列关于风力F与偏角θ、小球质量m之间的关系式正确的是（   ）

    Here is some information(信息) about some people.

    I am a math teacher. I teach math very well. Do you need help with your math？Call me at 679－ 8840.(Mr. Brown)

    I lost my blue bag. It's from my mom and I like it very much. Did you find my bag？Please call me at 777－8953.(Lucy)

    I like playing the violin，but I can't play it well. Can you help me？My phone number is 235－ 7765.(Joan)

    Do you like reading？I have many old books and the books are free. Call me at 658－0034.(Mark)

    Here is some information on today's newspaper.

    FOUND

    A blue bag. I found it in the library. My name is Sue. Please call me at 889－0764.

    JOB

    Are you good at math？Are you good with kids？We need a math teacher at our middle school. My name is Nick. My e－mail is nick@gmail.com.

    MUSIC CLUB

    Do you want to be a musician？Do you want to learn how to play the piano and the violin well？ Come to our club. Only 20 yuan for one lesson. Call Susan at 776－9898.

    BOOKS NEEDED

    We want to build a library for the kids in a small village. We need many books. Please call Mr. Han at 458－2217.