如图所示，放在水平面上的物体受一个斜向上、与水平面成θ角的拉力F，这个力的作用效果是什么？根据作用效果将力F分解，并求出分力的大小．

甲和乙两个物体在同一直线上运动，它们的v﹣t图象分别如图中的a和b所示．在t₁时刻（   ）

阅读理解
B
    I went to Paris last August．I went there with my friend Jeff．We went by train．We stayed for five days in a small hotel in the center of Paris. The hotel was not expensive .Our room was OK—it was old，but very clean.
    In the mornings we visited all the famous tourist sights(著名的旅游景点)and museums．The Louvre Museum was my favorite ! We usually had some bread for lunch in a park．In the afternoons we walked around Paris．We took a lot of photos! And we had crepes! They were delicious! After a little sleep and a shower, in the evenings．We had dinner in small restaurants and then we went to pubs(酒吧)．We met very interesting people! We also made some good friends．
    We didn't buy any gifts．Everything was very expensive．But we sent(邮寄)very beautiful postcards(明信片)to our friends．We had a lot of fun ! It was an excellent holiday!
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建国初期，***指出：“现在我们能做什么?能造桌子椅子，能造茶碗茶壶，能种粮食，还能磨成面粉，还能造纸，但是，一辆汽车、一架飞机、一辆坦克、一辆拖拉机都不能造。”这说明当时我国必须（    ）

你知道吗，自然界中的云、雨、雾、露、霜、雪、雹都是小水滴的“杰作”，海洋上空的水蒸气因为____投向了大海的怀抱，“调皮”的水滴因为____使河床干涸．（填物态变化名称）