题干

如图,轻质杠杆上各小格间距相等,O为杠杆中点.甲、乙是同种金属材料制成的实心物体,甲为正方体,乙重15N,将甲、乙用能承受最大拉力为20N的细线分别挂于杠杆上M、Q两刻线处时,两细线被拉直且都沿竖直方向,M、Q正好在甲、乙重心正上方,杠杆在水平位置平衡,这时甲对地面的压强为4000Pa;当把乙移挂至R时,甲对地面的压强为3750Pa.下列说法中正确的是(   )

A:金属块甲的重力为45N

B:金属块乙的体积为200cm3

C:将甲向右移动并挂于N正下方,乙仍挂于R,放手后杠杆仍能平衡

D:将甲向右移动并挂于P正下方,乙移挂至S,放手后甲被拉离地面

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答案(点此获取答案解析)

A,C

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阅读与回答问题
    Do you feel lonely when your best friend isn't around? Of course, yes. Here's our advice to you—and to all kids who feel lonely sometimes. 
You may feel lonely at break or lunchtime when a best friend isn't around—maybe because he or she moved to a different school or a different class. You want to have new friends, but how do you make them? Maybe it seems everybody else already has his or her friends. But remember, there's always room for more friends.
    Start by looking around your classroom—think about which kids you'd like to play with at break. Look for chances to say hi to them, smile, and be friendly. Offer to share something or express your appreciation (欣赏) to them. Invite someone to play with you or say, “Do you want to sit here?” in the lunchroom. When you're at break, walk over to kids you want to play with, act friendly, and say “Hi, can I play, too?” or just join in. 
     If you have trouble doing this or if you're feeling shy, ask your teacher to help you make new friends. Teachers are usually pretty good at matching up friends. The best way to make friends is to be a friend. Be kind, be friendly, share, say nice things, offer to help ---and pretty soon, you'll have one, or two, or even more new friends.
    You might still miss that special best friend. But when you see each other, you can share something you didn't have before he or she left. You can introduce him or her to your new friends!