A doctor was allotted into a research center and became the man with highest education qualification.

One day, he went to a little pond behind the center for fishing, on the beam, the superintendent and vice superintendent was fishing too. He nodded slightly at them and thought: what are you talking about, you two undergraduates.

After a while, the superintendent put down the fish pole, gave a stretch and walked to the toilet from the water surface. The doctor was so surprised that he almost can’t believe his eyes. Floating on water surface( 水上飘)? It must not be true? This is a real pond!

The superintendent came back from the water surface as well.

What's the matter? The doctor felt embarrassed to ask, he was a doctor!

After another while, the vice superintendent stood up and walked to the toilet from the water surface as well. It almost made the doctor faint: it must not be true! Am I at a place full of master?

The doctor wanted to go to the toilet too, but the pond had fence at each side, it would take much more time if bypass the pond. What should I do?

The doctor was unwilling to ask the two superintendents, hold a long while, he stepped into the water: I disbelieve that the undergraduates can cross the while I, a doctor can’t.

With a sound, the doctor fell into the water.

The two superintendents pulled him out off the water and asked why he dropped into the water. He asked: why you can walk across the pond? The two looked at each other and smiled: there are two lines of stakes in the pond below the water surface because of swelling after two days of rain. We all know the stakes’ exact locality, can step on the stakes and cross the pond. Why you don’t ask us?