Q: What causes the white smoke behind airplanes?
A It is actually water vapor. Water is a by-product of combustion. The "contrails" occur at specific altitudes each day depending on the atmospheric conditions.

Q: How high is the tallest control tower?
A: The world's highest control tower is Vancouver Harbour Control Tower, situated on top of the 142 meter skyscraper 200 Granville Square, in downtown Vancouver, Canada. The world's tallest free standing control tower is the 132.2 m (434 feet) Suvarnabhumi Airport control tower, 25 km east of Bangkok, Thailand