Which two situations may introduce locking errors for Ursa Major Solar?

Every day, Ursa Major Solar uploads a large number of parent and child records into Salesforce to maintain integrations with other systems that update their data in scheduled batches or continuously in real time. Ursa Major Solar is concerned about locking errors.

Which two situations may introduce locking errors for Ursa Major Solar? (Choose two.)
A . Updates to parent records and their child records being processed simultaneously in separate threads
B . Updates to child records that have the same parent records are being processed simultaneously in separate transactions
C . Updates to parent and child records are being processed synchronously in the same threads
D . Updates to parent and child records are being processed in the same batch

Answer: A,B