Can you arrange four 9's and use at most 2 math symbols, to make the total 100?

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

The following sentence is false. The preceding sentence is true.
Are these two sentences true or false?

Move three sticks of the spiral below to form a square.

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?

What does it mean?

Can you name an animal whose killing cannot be performed without spilling your own blood?

Spot the 3 Differences in the given Picture.

100 prisoners are stuck in the prison in solitary cells. The warden of the prison got bored one day and offered them a challenge. He will put one prisoner per day, selected at random (a prisoner can be selected more than once), into a special room with a light bulb and a switch which controls the bulb. No other prisoners can see or control the light bulb. The prisoner in the special room can either turn on the bulb, turn off the bulb or do nothing. On any day, the prisoners can stop this process and say "Every prisoner has been in the special room at least once". If that happens to be true, all the prisoners will be set free. If it is false, then all the prisoners will be executed. The prisoners are given some time to discuss and figure out a solution. How do they ensure they all go free?

A quarter is one-fourth of a dollar but Mr. John has changed the equation as below :

DOLLAR * 4 = QUARTER

Can you replace each letter with a digit to make the above solution correct?