在一山顶有铁塔AB，从点P到铁塔底部B点有一条索道PB，索道长为300米，与水平线成角为α=30°，在P处测得A点的仰角为β=45°，试求铁塔的高AB．（精确到0.1米，其中$\sqrt{2}$≈1.41，$\sqrt{3}$≈1.73）

CuO和Cu（OH）₂固体混合粉末20g，其中铜元素的质量分数为72%，放入一定量的稀硫酸中，恰好与两种固体完全反应，反应后形成溶液的溶质质量分数为18%，则加入稀硫酸的溶质质量分数为（　　）

    Last Friday was a cold day, and the bus was due to come in about 15 minutes. So I went to the nearby convenience store and came back to the station where a junior high school girl was still there,____ (wait) for the bus too. I gave her one of the two warm cocoa ____(can) I bought and we had a little talk ____ warming our hands with the hot cocoa.

    She ____(have) her high school entrance exam in a week so I told her a few encouraging words. I left her happy, she thanked me, and told me she wished ____(see) me again. I smiled and thanked her very____(grateful), nodding yes, the bus had already stopped and I had to hurry away.

    We may never see each other again but I am grateful to her ____ saying "wish I could meet you again" as ____takes a strong will, and courage to accept an offering from a stranger. That young girl helped me more than I could have helped her. I ____(touch) with a memory and a reason to send all the kids ____ this very moment are full of emotions and fears, wishes of good luck and many bits of love.