What occurs twice in a week, once in a year but never in a day?

There was once a college that offered a class on probability applied to the real world. The class was relatively easy, but there was a catch. There were no homework assignments or tests, but there was a final exam that would have only one question on it. When everyone received the test paper it was a blank sheet of paper with a solitary question on it: 'What is the risk?'.Most students were able to pass, but only one student received 100% for the class! Even stranger was that he only wrote down one word!
What did he write?

How is the moon similar to a dollar?

A man was driving a black truck. His lights were not on. The moon was not out. A lady was crossing the street. How did the man see her?

In the following picture, E is going to slide the object down and as per the terrain and the physics, the round object is going to travel all the way till the end. Now, can you analyze who all people will die when it happens?

Find the missing number in the sequence below:

I make a loud sound when I’m changing. When I do change, I get bigger but weigh less. What am I?

Do You See It?

When can we add 2 to 11 and get 1 as the correct answer?

You measure my life in hours
I serve you by expiring
I vanish faster when I am thin
and slower when I am thick
The wind is my energy
What am I?