题目

Human beings have used tools for a very long time. In some parts of the world you can still find tools that people used more than two million years ago. They made these tools by hitting one stone against another. In this way, they broke off pieces from one of the stones. These chips of stone were usually sharp on one side. People used them for cutting meat and skin from dead animals, and also for making other tools out of wood. Human beings needed to use tools because they did not have sharp teeth like other meat eating animals, such as lions and tigers. Tools helped people to get food more ea抛物线y2=4x的焦点为F，准线为l，则过点F和M（4，4）且与准线l相切的圆的个数是（　　）A．0B．1C．2D．4