What does this rebus puzzle means ?

What are the next two letters in the following series and why?
W A T N T L I T F S _ _

*Hint: Check Puzzle Title

You have 10 balls with you. A friend of yours out of nowhere asks you to place those ten balls in five lines such that each of the lines has exactly 4 balls on them. He needs to check your intelligence. Prove him by doing the task.

It has five wheels, though often think four, You cannot use it without that one more, You can put things in it, you can strap things on top, You can't find it in the market, but you can still go shop. What is it?

By including only four matchsticks in below picture, you have to make "Four Triangles And Two Squares"

I speak without a mouth, and hear without ears. I have no-body, but I come alive with the wind. What am I?

What runs around the whole yard without moving?

Find the next number in the sequence

5 12 24 36 ?

If you drop a 15 kg iron bar and a 5 kg bag of cotton from a height of 50 meters which will reach the ground first?

Why Aeroplane windows are round?