Ques:Q: What thin layer of air acts as a barrier to prevent cool air from mixing with warm air in the stratosphere? Read this paragraph and choose the correct option from the provided answers: At the top of the troposphere is a thin layer of air called the tropopause. You can see it in Figure above . This layer acts as a barrier. It prevents cool air in the troposphere 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? Read this paragraph and choose the correct option from the provided answers: Plants don't have immune systems, but they do respond to disease. Typically, their first line of defense is the death of cells surrounding infected tissue. This prevents the infection from spreading. Many plants also produce hormones and toxins to fight pathogens. For example, willow trees produce salicylic acid to kill bacteria. The same compound is used in many acne products for the same reason. Exciting new research suggests that plants may even produce chemicals that warn other plants of threats to their health, allowing the plants to prepare for their own defense. As these and other responses show, plants may be rooted in place, but they are far from helpless. 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? Read this paragraph and choose the correct option from the provided answers: A newborn baby has a soft spot on the top of its head. Over the next few months, the soft spot gradually hardens. What explains this?. 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? Read this paragraph and choose the correct option from the provided answers: Most of the rocks and minerals that make up the Earth's crust are composed of positive and negative ions held together by ionic bonding. An ionic compound is an electrically neutral compound consisting of positive and negative ions. You are very familiar with some ionic compounds such as sodium chloride (NaCl). A sodium chloride crystal consists of equal numbers of positive sodium ions (Na + ) and negative chloride ions (Cl ). Choices: - correlated compound - isotope - neutralized molecule - ionic compound A:

Ans:
ionic compound
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