Placid because it is used to describe the ducks
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.
Answer:
Impudence's meaning is not showing due respect for another person; impertinent, insolent. I highly doubt that a person who is impudent with others could ever cool off a tense situation. They would have to change their attitude towards others to be able to calm down.
For example, "the student is being impudent with his teacher".
It is the center of the earth