What is the best definition of a “blitzkrieg”? devastating airplane attack
rapid invasion by air and land
attack by multiple infantry troops
destruction of airplanes and tanks

In this context, the best definition of “blitzkrieg” is a  rapid invasion by air and land.

The term "Blitzkrieg" is a combat term that describes an offensive warfare designed to strike a focused blow at an enemy using either a mobile forces, maneuverable forces, armored tanks, air support etc.

Thus, the best definition of “blitzkrieg” in this context is a rapid invasion by air and land.

Therefore, the Option B is correct.

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According to the sentence, the best definition of “blitzkrieg” is include option B: a rapid invasion by air and land.

The term "Blitzkrieg" refers to as an offensive warfare in which enemies using either a mobile forces and armored tanks etc. in order to do war activities.

Blitzkrieg was invented by Heinz Guderian before the World War 2. He was the member of German military.

Therefore, the Option B is correct.

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the correct answer is b, "fertility rates are increasing, so populations will grow more quickly in the future."

a because i tried to vote with just my college id and the answer was no