如图，⊙O的半径为2，弦AB⊥OC于C，AB= $2\sqrt{3}$ ，则OC等于（　　）

    Today is Children's Day.The students are in the park.There's a hill and a lake in the park.Now it's lunchtime.They're having a picnic on the grass.Zhang Tao is having a hamburger,Li Ming is eating a hot dog, Wang Lan is drinking some orange juice.They are going to to go skating after lunch.They can't find Su Hai and Su Yang.Oh,they're flying kites over there.All the students are very happy.

我国512家最大的国有骨干企业占国有骨干企业占国有工业企业总数不到1%，而资产量占55%，销售收入占60%以上，向国家提供的利税占85%。当前，我国国有资产在能源、铁路运输、钢铁和邮电通信等产业中的比例分别高达95%以上。这表明（       ）

观察如图，从生物体结构层次上分析，与其他三幅图不同的是（  ）