A subject enrolled in a drug clinical trial has withdrawn from the study.

Theprotocolgoverns all trial conduct, including whether subjects should be replaced when they withdraw.

ICH E6(R2) 6.0:The protocol must contain “detailed information on trial design, methodology, statistical considerations, and the organization of the trial.”

ICH E6(R2) 6.9.2:The section on “Subject withdrawal or discontinuation” specifies “whether and under what conditions subjects may be replaced.”

Other documents serve different functions: the DSM plan (A) manages safety oversight, the IB (C) summarizes product background, and the consent form (D) explains subject rights but does not guide study conduct. Only theprotocolprovides the operational answer regarding replacement.

Thus, the correct answer isB (The protocol).