I think the answer is C, I could be wrong. Let me know if I am right!
Have* this is because has* is past tense and have is more appropriate since there are multiple things you are referring too (Mercury, Venus, Earth and Mars). To be honest, these planets have a molten core.
I think it's 76,000. maybe
It can affect your life in the business world in a lot of ways. If you have good rhetoric, you're more likely to be hired and you'll probably perform better since you'd be more persuasive and eloquent.
If you have poor rhetoric, you're probably less likely to be hired because you don't know the vocabulary or you're not very persuasive. You also might perform poorly (for instance if you had to sell something and you didn't have good speech)
