Solution

What causes the movement of the egg into the bottle? (pick the right answer).

a) When carrying heavy luggage for a long time it gets heavier an heavier until one is not able hold it anymore. The egg also gets heavier until it drops into the bottle by its own weight.

b) The generated vaccum inside the bottle sucks the egg in.

c) Due to heating the bottle contains hot air. When the air cools down after putting the egg onto the bottleneck, the air pressure inside the bottle deteriorates. And since the external air pressure is higher the egg is being forced into the bottle.

d) The egg closes the bottle up. While cooling down the air volume deteriorates causing a cavity sucking in the egg.