Which sentence, if added after sentence 6, would best create a strong, descriptive image that helps to explain why Rachel feels comforted?She was young yet carried herself with great confidence, and her clear eyes locked onto mine and oozed kindness. Dr. Perez was the youngest-looking dentist I had ever seen. She looked to be only a few years older than me.
I knew that I would like Dr. Perez and would never again be so anxious before a dentist appointment.
Dr. Perez moved quickly around the room, quietly gathering her dental tools.

She was young yet carried herself with great confidence, and her clear eyes locked onto mine and oozed kindness.

Explanation:

The second option states she knew she would like the dentist and would never be so anxious again, but it isn't a 'descriptive image that helps explain why Rachel feels comforted.' Generally, when we see a person close to age engaging in an activity that would otherwise make us nervous, we involuntarily relax -- because if they're cool, why wouldn't we be too, so the second option is probable, but not everyone is aware that our brains work that way.

The first option, though, clearly and descriptively gives Rachel a reason to be kind -- the dentist's eyes are kind and clear.