What could be the reason for this problem?

Universal Containers (UC) is a non-profit organization and has over 20,000,000 members (donors). The company decided to assign those accounts to Donations Reps based on their regions. Donations Reps ended up owning over 50,000 donors each. The donation reps started to see significant degradation of the system performance.

What could be the reason for this problem?
A . The Donations Reps access to the assigned accounts.
B. Salesforce sharing recalculation kicked off.
C. There is an Account ownership data skew problem.
D. The Account (donor) object OWD is Private.

Answer: C