Sentence 6

"She looked like a successful matron on her way out for lunch at her favorite club. But her eyes, as vivid a blue as his own, were filled with concern." -from Hidden Riches by Nora Roberts

Roberts uses a conjunction to begin her next sentence to show a contradiction to cool, aloof exterior of the grandmother.

My example: The teenager had an impeccable resume- flawless GPA, full extracurricular schedule. But he just asked if Thailand was in China.