阅读下列图文资料，回答问题。

材料一：2011年3月11日，日本仙台港以东太平洋附近海域（约北纬38.1°，东经142.6°）发生里氏9.0级特大地震并引发巨大海啸。

材料二：温家宝总理2011年5月21日至22日出席了在日本东京举行的第四次中日韩领导人会议，三国领导人就中日韩合作和共同关心的地区及国际问题深入交换了意见。

根据短文理解，选择正确答案。

    Do you know pigeons? They are a kind of birds. They are in white and grey. Some people say they are not beautiful but they are cute and smart. Many people keep them as pets. Why do people say pigeons are clever? Because pigeons can take letters from one place to another. And they know the way home. We often see the picture of a pigeons with an olive branch(橄榄枝) in its mouth. We call them peace pigeons. They are the symbol of peace.

下列关于高分子化合物的组成、结构、性质的说法正确的是(　　)

以下事件发生在1950年的有（    ）

①开国大典 ②西藏和平解放 ③抗美援朝战争爆发 ④土地改革运动的开始