The best and most correct answer among the choices provided by your question is the fourth choice or letter D "The thin membrane that closes the cavity of the middle ear from the outside changes position."
Your ears pop in airplanes because the air high above the surface of Earth is less dense than air near the surface, because air near the surface has all the air above it pushing down. Your inner ear has air trapped in it and as the atmospheric pressure changes, it causes pressure on your eardrum.
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You can't put sodium metal and chlorine gas on your fish and chips.
Explanation:
Sodium is an electron rich metal. Chlorine is an oxidizing gas. Put them together, and they form a salt, a compound of a metal and a non-metal. Hope it helped!!
