Clean riddles

A kind hearted person Mr. Rawat buy packed food at 3$/packet from United states and sells them at 1$/packet at Africa. After some time he becomes a millionaire. How come the guy become millionaire?

I repeat only the last word you say. The more I repeat, the softer I got. I cannot be seen but can be heard. What am I?

What is the shortest complete sentence in the English language?

I have seas without water. I have forests without wood. I have deserts without sand. I have houses with no brick. What am I?

Give me food, and I will live. Give me water, and I will die. What am I?

What is the longest word in the dictionary?

Four men were fishing in a boat on the lake. The boat turned over and all four men sank to the bottom of the lake. And yet, not one single man got wet. How is this possible?

I am not alive but I grow. I don't have lungs but I need air. What am I?

In a supermarket, the first 25 customers of the day purchased an average of two items each. After a further 15 customers, the average number of items purchased by each customer rose to eight. What was the average number of items purchased by the last 15 customers only?

I am a mother and a father, but have never given birth. I'm rarely still, but I never wander. What am I?