小华把一块无色透明的塑料片放在报纸上，并在塑料片上滴一滴水，这样就能把报纸上的小字放大．这滴水相当于一个______．

A．It shocks the audience.

B．It is a realistic situation drama.

C．It is the first programme that tells about the Cockney way of life.

D．It deals with the problems other similar programmes have not done before.