Both sentences with true grammar are C and D. Let me tell you what is wrong with each. a. The comma is forgotten in front of the word unicorns. b. The word unicorns is misspelled! C and D are the exact same sentence, and they are both correct! Hope this helped!
Safe is the best option but it could also be wary or even rash as well but it's more likely to be safe and if that's not the correct word choice then it's a safe bet wary is the correct possible alternative hope this helps you out!