Answer: B. Needs the current Xact to finish before another one starts.
Step-by-step explanation:
A serial schedule is a schedule whereby for a transaction to start, one must be completed first. The transactions are done one after the other.
In this case, when the cycle of a transaction have been completed, then the next transaction can begin. Therefore, the answer will be option B "needs the current Xact to finish before another one starts".