如图，两个同心圆的半径分别为4cm和5cm，大圆的一条弦AB与小圆相切，则弦AB的长为（　　）

下列关于单细胞生物的相关叙述中，不正确的是（　　）

    Mr. Black takes his daughter 1 a restaurant. They sit down, and there are a lot of  2 in the restaurant. They 3 for a long time, but no waiters come to their table.

    Mr. Black says, "I'm 4, I can't wait." He waits for a minute and says, "Now I am going to 5 something to get a waiter soon."

    He goes out of the restaurant and 6 the restaurant, "My 7is at a table in your restaurant, she 8 a red hat."

    The waiter finds the girl and he says to Mr. Black, "Yes, she's here. Do you want to 9 her?"

    "No," says Mr. Black, "But please give her something to eat quickly. She is very 10". Then he goes back to the restaurant. He is glad to see that a waiter is now at this table.