In accordance with the CFR, the sponsor (who is not a sponsor-investigator) is responsible for...

Sponsors are responsible for distributing safety updates across all investigators and the FDA.

21 CFR 312.55(b):“The sponsor shall promptly notify all participating investigators, and the FDA, of new significant adverse effects or risks with respect to the drug.”

Other responsibilities fall elsewhere:

Case histories (C) are maintained by investigators (21 CFR 312.62(b)).

Progress reports to IRBs (D) are the investigator’s duty (21 CFR 312.66).

Administration of investigational drug (A) is managed by the investigator at site level.

Thus, the correct answer isB (Ensuring FDA and investigators are promptly informed).