Which code segment should you use?

You need to update the ImportBooks() method to use database transactions.
Which code segment should you use?
A. SqlConnection.BeginTransaction(IsolationLevel.RepeatableRead);
B. SqlConnection.BeginTransaction(IsolationLeve.ReadUnconvnited);
C. SqlConneetion.BeginTransaction(IsolationLevel.Serializable);
D. SqlConnection.BeginTransaction(IsolationLevel.Snapshot);