Name the American soul singer whose best-known tunes include "Think" and "Respect."

The American soul singer best known for "Think" and "Respect" is Aretha Franklin. She is often referred to as the "Queen of Soul" and made significant contributions to music, particularly in the genres of soul and R&B. Her powerful, emotive voice and style helped to define the sound of soul music in the 1960s and beyond. Aretha Franklin's rendition of "Respect," originally written and recorded by Otis Redding, became an anthem for the feminist and civil rights movements.

"Think," another one of her iconic songs, showcases her vocal range and depth as an artist. Aretha's impact on music and culture has been profound, earning her numerous awards, including multiple Grammy Awards, which further solidifies her legacy as a musical icon. The other options listed do not align with the songs mentioned; Nina Simone and Billie Holiday, while influential singers, do not have "Think" or "Respect" in their known repertoire.