Answer: The right answer is the A) His heel.
Explanation: Just to elaborate a little on the answer, it can be added that, when he was a baby, Achilles was immersed by his mother in the River Styx, because its water allegedly granted the power of invulnerability. She did so in order to protect him, since it had been predicted that he would die at a young age. However, by holding him by the heel, she neglected to dip that part of his body, and he was eventually killed by a poisounous arrowed that pierced his heel.
