A stem-cell niche is an area of a tissue that provides a specific micro-environment, in which stem cells are present in an undifferentiated and self-renewable state.
Answer:
Cold, dense air squeezes its way through the warmer, less-dense air, and lifts the warm air. Because air is lifted instead of being pressed down, the movement of a cold front through a warm front is usually called a low-pressure system.
Explanation:
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The answer is C barriers around mating
