The use of 2 violins, 1 viola, and 1 cello as a group became one of the most important instrumental combinations throughout the Classical and Romantic periods. This specific group of instruments is known as a

it's d. (also remember it's produced physically,visual effects )

i believe it is a. a segment : )

variety in color and variety in texture

the answer is counterpoint.

counterpoint definition: "the art or technique of playing a melody or melodies in conjunction with another, according to fixed rules."

counterpoint is present in a lot of baroque music- such as bach (notably his wtc prelude and fugues) and scarlatti, but can also be found in music by mozart, beethoven. it can even be found in music as modern as john williams!