What could be the technical reason for this?

Universal Containers has built a recruiting application on the salesforce Platform. HR requested that all internal users should have edit access to the referral customobject. One of the recruiters needed to share a referral record with another colleague for collaboration using manual sharing. The recruiter opened the referral record and could not find the share button.

What could be the technical reason for this?
A . The Referral object OWD is private.
B. The Referral object OWD is public Read/Write.
C. The Referral object OWD is public Read only.
D. The Referral object OWD is public Full Access.

Answer: B