It's a protector.
It sits on a bridge.
One individual can see directly through it, while others wonder what it hides.

What is it?

If eleven plus two equals one, what does nine plus five equal?

A doctor and a boy were fishing. The boy was the doctor’s son, but the doctor was not the boy’s father. Who was the doctor?

How much will a 38° angle measure when looked at under a microscope that magnifies ten times?

A father is locked up in jail. His wife has gone bankrupt. Their male child has to sell his hotel in order to gain some money. Yet their girl child does not care and is quite happy.

How can someone be so rude?

What is the word or phrase?

Two boys were admitted to a school. When the headmaster asks them about their parents, they tell him that they have same parents (father and mother). On further inquiry, it turns out that they both share the same date for their birthday.

"Are you twins," ask the headmaster.
"No," replies the boys.

Is it possible?

A king sentenced a man to the death sentence for some crime he had committed. Known for his kindness, the king told the culprit that he had a choice to die in a way he decides.

The culprit was clever and said something that saved him from death. What method do you think he must have chosen for his death?

10+10 and 11+11 can give you the same answer.

Explain how?

You have a three-gallon and a five-gallon measuring device. You wish to measure out four gallons.