Final answer:
A viola is included in a String quartet, which generally features two violins, a viola, and a cello.
Step-by-step explanation:
The type of ensemble that includes a viola is a String quartet. A string quartet typically consists of two violins, one viola, and one cello. Ensembles are organized based on the types of instruments they include. While brass ensembles are composed of brass instruments like trumpets and trombones, woodwind quintets include woodwind instruments such as flutes, clarinets, oboes, bassoons, and possibly a French horn. Percussion ensembles include various percussion instruments such as drums, xylophones, and cymbals. The only type of ensemble listed that includes a viola is the string quartet, which consists of two violins, a viola, and a cello. So the correct answer is Option 2: String quartet.