What goes up but never comes down?

Can you replace the X (both small and big x) with the numbers between 1 to 19 such that all the rows of 3 numbers between X (big x) sum to 23?

How many bananas can you eat if your stomach is empty?

Why do Chinese men eat more rice than Japanese men do ?

What's the best place to go shopping in the ocean?

What's the only room from which no one can enter or leave

You are in a land where thirty men and two women were dressed in classic black and white dresses.
They begin to fight as soon as any of them move.

Where are you?

You board a train. The train will have to enter a tunnel soon. You are claustrophobic. Which place is the best for you to sit?

I sleep during the day and fly at night, but I have no feathers to aid my flight. What am I?

Replace the question mark in the picture below.