What are the three riddles in opera nessun Dorma and what answers?

The three riddles in the aria "Nessun Dorma" from the opera Turandot by Giacomo Puccini are:

1. Enigma primo: "In the starry night, what sings?"

Answer: "The Princess Turandot's tears."

2. Enigma secondo: "On ice that burns, which flame glows?"

Answer: "Turandot's frozen heart."

3. Enigma terzo: "What is born and never dies?"

Answer: "Love."