Final answer:
The passage from "Marian Anderson Sings" is likely included to highlight discrimination and the obstacles Anderson faced due to the white performers only policy of the Daughters of the American Revolution, not because of her popularity or the venue's booking schedule.
Step-by-step explanation:
The author includes this passage in "Marian Anderson Sings" to highlight the challenges that Marian Anderson faced when trying to book a performance at Constitution Hall. Despite her manager's efforts to secure a date, they were persistently told that no dates were available. This passage serves to underscore the racial discrimination Anderson faced, as Constitution Hall was controlled by the Daughters of the American Revolution (DAR), who had a white performers only policy. This policy was publicly challenged leading to Eleanor Roosevelt's resignation from the DAR and eventually to the historic concert at the Lincoln Memorial on Easter Sunday, April 9, 1939.
The correct answer is: a. to show how difficult and competitive the music business can be. This answer is chosen over the others as the passage indicates that Anderson's manager encountered repeated rejections, which suggests a deliberate attempt to prevent Anderson from performing, likely due to the racial prejudices of the time, rather than a reflection of her popularity or the venue's general booking status.