将表Teacher中职称字段为"助教"人员改为"讲师"，应为______。

A：UPDAT E Teacher SET 职称="助教" WHERE 职称="讲师"

B：UPDAT E Teacher SET 职称="讲师" WHERE 职称="助教"

C：UPDAT E SET 职称="助教" WHERE 职称="讲师" FROM Teacher

D：UPDAT E SET 职称="讲师" WHERE 职称="助教" FROM Teacher