单项选择题

A. The shutdown proceeds immediately. The shutdown proceeds as soon as all transactions in the PDBs are either committed or rolledhack.
B. The shutdown proceeds as soon as all transactions in the CDB are either committed or rolled back.
C. The shutdown proceeds as soon as all transactions in both the CDB and PDBs are either committed or rolled back.
D. The statement results in an error because there are open PDBs.