Count The number of F's in the paragraph below:

"FINISHED FILES ARE THE RESULT OF YEARS OF SCIENTIFIC STUDY COMBINED WITH THE EXPERIENCE OF YEARS"

I am looking for a word that change both gender and number when i add the letter 'S'.

What Word am I Looking For ?

What have one eye but still cannot see?

I am a white box having no key or lid.
Yet there is a golden treasure inside it.

What Am I?

I am a type of food that is often found in the fridge and can be white in colour. What I am?
Hint 1: I am a dairy product.
Hint 2: You can spread me on the bread.

Before Mount Everest was discovered, what was the highest mountain in the world?

What has one letter and starts with an E?

Two in a corner, one in a room, zero in a house, but one in a shelter. What is it?

I am dry when I go inside, but wet when I am pulled outside.
The longer I am inside, the stronger I get
When I am completely out, I am wet and I literally sag
Who am I?

A man calls his dog from the opposite side of a river. The dog crosses the river without a bridge or a boat and manages to not get wet. How is this possible?