Jim：Hi, Kate！What's the weather like in Shanghai today?

Kate：Hi, Jim！It's sunny and warm here. I'm going to the zoo this afternoon.

Jim：Sounds good.

Kate：Jim, how's the weather in Beijing now?

Jim：It's cloudy. It's going to rain. So I can't fly a kite in the park.

Kate：Oh, I see.

Jim：Do you know the weather in Guangdong?

Kate：It's too hot. The children there usually go swimming in the river.

Jim：Oh, I like swimming, too. But I can't swim now. It's cold here.

工厂里生产的薄铁皮是卷成圆筒形的，为了计算铁皮的总长度，先剪下长为l的一段铁皮，称得它的质量为m，再称得整筒铁皮的总质量为M，那么铁皮的总长度L应为（  ）

春  望

杜  甫

国破山河在，城春草木深。

感时花溅泪，恨别鸟惊心。

烽火连三月，家书抵万金。

白头搔更短，浑欲不胜簪。