Explanation:

The blank must capture why Randall remains unknown despite her revolutionary contributions. The colon introduces an explanation: her work leaves "no trace in public consciousness," yields "no monument," and earns "acknowledgment only in footnotes." This describes work that is unrewarding in terms of public recognition - in other words, thankless.
- A. tenacious - describes persistence, which might characterize Randall herself, but not the nature of the work that explains her obscurity.
- B. thankless - perfectly captures work that receives no gratitude, recognition, or public reward.
- C. divisive - means causing disagreement; nothing in the passage suggests controversy.
- D. meteoric - means rapid and spectacular; the opposite of obscure, footnote-bound scholarship.
- E. collaborative - nothing indicates her work was or wasn't collaborative, nor would that explain her obscurity.