Final answer:
The grape boycott led by Cesar Chavez substantially helped to improve working conditions for farmworkers in California, securing better contracts with grape growers.
Step-by-step explanation:
The grape boycott of the DiGiorgio Corporation, organized by Cesar Chavez and the United Farm Workers (UFW), had a significant impact on the agricultural industry. The most accurate statement that describes the effect of the grape boycott is: (a) It helped to improve working conditions for farmworkers in California. Through a combination of labor strikes and consumer boycotts, the UFW convinced US consumers to only purchase produce from growers who recognized the union. This pressure led to improved contracts between California grape growers and farmworkers, with benefits that included better pay and working conditions, making a lasting impact on migrant laborer's lives.