It is also the fifth-largest in the nation,[68] with approximately 3,500 students completing a co-op each year at over 2,000 businesses.[69] The program requires (or allows, depending on major) students to work in the workplace for up to five quarters alternating with quarters of class. The amount of co-op varies by major, usually between 3 and 5 three-month "blocks" or academic quarters. Many employers prefer students to co-op for two consecutive blocks, referred to as a "double-block co-op".