—Hi, Jack! I never thought I would meet you here. _______?

—Fine. Thank you. And you?

A．How is your job

B．How are you getting on with your new job

C．Lovely weather, isn't it

D．How are you

多个事务在某个调度下的执行是正确的，是能保证数据库一致性的，当且仅当该调度是【 】。