In accordance with the ICH GCP Guideline, who is responsible for the accuracy, completeness, legibility,...

The investigator holds ultimate responsibility for all data reported.

ICH E6(R2) 4.9.1:“The investigator is responsible for the accuracy, completeness, legibility, and timeliness of the data reported to the sponsor on the CRFs and all required reports.”

Monitors (D) verify data accuracy but are not responsible for data quality. Quality specialists (B) and IRB staff (C) have no role in data entry.

Correct answer:A (The clinical investigator).