The answer is D. Sentence 7. When it says "plates may also collide", it is bringing up another topic about the plates. As you read past sentence 7, you notice a shift in topic as you are reading. Instead of plates sliding against each other, the speaker is now talking about them colliding.
That would be a noun. Proper nouns are more specific, and are often capitalized. For example, HE would be a noun, but if you were to say JOHN it'd be a proper noun.
Answer:
Each stanza compares wind, water, and stone to the powers of the other to see which is the most powerful and which ability can overcome the most. Overall the poem is about how nature has effects on everything. The poem states that wind changes the water but stone can move water and wind can be in water.
