Ques:Q: What thin layer of air acts as a barrier to prevent cool air from mixing with warm air in the stratosphere? Choices: - methosphere - endosphere - liposphere - tropopause A:

Ans:tropopause
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Ques:Q: What do willow trees produce to kill bacteria? Choices: - chlorophyll - enzymes - cytoplasmic acid - salicylic acid A:

Ans:salicylic acid
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Ques:Q: A newborn baby has a soft spot on the top of its head. over the next few months, the soft spot gradually does what? Choices: - weakens - grows - shrinks - hardens A:

Ans:hardens
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Ques:Q: What is an electrically neutral compound with positive and negative ions? Choices: - correlated compound - isotope - neutralized molecule - ionic compound A:

Ans:
ionic compound
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