香港、澳门特别行政区位于美丽富饶的珠江三角洲，这里气候湿热，四季常青；经济繁荣，风景优美。根据所学知识，回答下列各题。

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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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面对色彩斑斓的网络文化世界，近年来我国深入开展整治互联网和手机媒体淫秽色情及低俗信息等行动。开展这一行动可以帮助青少年：
①提高辨识能力，抵制腐朽文化
②崇尚流行文化，培养健全人格
③维护文化安全，坚持多元指导
④陶冶道德情感，升华思想境界

两根光滑的金属导轨，平行放置在倾角为θ的斜面上，导轨的左端接有电阻R，导轨自身的电阻可忽略不计．斜面处在匀强磁场中，磁场方向垂直于斜面向上．质量为m、电阻可不计的金属棒ab，在沿着斜面与棒垂直的恒力F作用下沿导轨匀速上滑，并上升h高度．如图所示，在这过程中（   ）

设 $P$ 是双曲线 $\frac{x^2}{a^2}-\frac{y^2}{b^2}=1$ （ $a>0$ ， $b>0$ ）上的点， $F_1$ 、 $F_2$ 是焦点，双曲线的离心率是 $\frac{5}{4}$ ，且 $\angle F_{1}P{F}_2=90°$ ， $\Delta F_{1}P{F}_2$ 面积是9，则 $a+b=$ （    ）