如图，△ABC中，∠C=90°，AC=3，AB=5，D为BC边的中点，以AD上一点O为圆心的⊙O和AB、BC均相切，则⊙O的半径为____．

用括号内所给动词的适当形式填空。
The garden is the best place ____ (grow) flowers.
This pair of jeans ____  (match) his white shirt.
Listen! How wonderful the music____ (sound) ！
 Mary, ____  (not be) afraid of the dog. It never bites.
 Keep quiet, the students ____ (prepare) for the coming exam.
____  (ride) a bike to school is good for your health.
Sandy spends a lot of time____  (chat) with her e-friend on the Internet.
How long does it take you____ (walk) to school every day?
I don’t have any ideas, I don’t know where ____ (go).
Would you like____ (drink) a cup of tea?

虽然中国经济增长“换挡降速”，面临严峻挑战，但改革依然“快马加鞭”。改革开放的30多年，是我国经济快速发展的30多年，同时也是中华文化伟大复兴的30多年，是中国文化事业繁荣发展的30多年。30多年来，我国文艺创作日益繁荣，文化市场和文化产业蓬勃发展，文化体制改革不断深化，文化建设的保障体系更加完善。

请简要分析上述材料体现了文化生活哪些道理。

在匀强磁场中，有一根长0.4m的通电导线，导线中的电流为20A，这条导线与磁场方向垂直时，所受的磁场力为0.015N，求磁感应强度的大小．