Which instruction provides the SRB entitlement guidance for STA-21 students?

The correct answer is indeed B, OPNAVINST 1160.6A. This instruction specifically outlines the policy and procedures regarding the Seaman to Admiral (STA-21) program, which includes entitlement guidance for the Selective Reenlistment Bonus (SRB) for students participating in this program. It ensures that those enrolled in STA-21 are aware of the benefits and eligibility requirements associated with their status, ensuring clarity and proper understanding of their financial entitlements while they pursue their educational goals.

In the context of the other options, OPNAVINST 1150.3A deals with naval personnel policy management but does not specifically address SRB for STA-21 students. BUPERSINST 1780.1 pertains to various enlisted advancements and may touch on bonuses, but it doesn't directly focus on the STA-21 program or SRB entitlement as it relates to those students. NAVADMIN 210/21 provides updates or announcements that may affect personnel policies but does not serve as the primary guidance document for SRB specifically for STA-21 participants. Thus, OPNAVINST 1160.6A is the definitive source for this information.