这个蛋糕是妈妈做的 I think this is a special use of the 是…的 construction to indicate the 'passive voice'. The 'active voice' would be: 妈妈做了这个蛋糕 (The subject of the verb is the doer of the action.) The 'passive voice' is usually marked with 被. So the top statement could also be expressed as: 这个蛋糕被妈妈做了 This is grammatically correct, but would not really be used, because 被 often suggests a bad action. For example, we could correctly say: 这个蛋糕被我的狗吃了 = "This cake was eaten by my dog"
非常感谢！ 对我很大的帮助！ 您说的很标准，很了解。 谢谢♥️
这个蛋糕是妈妈做的
I think this is a special use of the 是…的 construction to indicate the 'passive voice'.
The 'active voice' would be:
妈妈做了这个蛋糕 (The subject of the verb is the doer of the action.)
The 'passive voice' is usually marked with 被.
So the top statement could also be expressed as:
这个蛋糕被妈妈做了
This is grammatically correct, but would not really be used,
because 被 often suggests a bad action.
For example, we could correctly say:
这个蛋糕被我的狗吃了 = "This cake was eaten by my dog"
谢谢您的回复。
“被”字句的动词一般都有动作性动词，所以不说“这个蛋糕是被妈妈做的”。可以说“这个蛋糕是被妈妈吃的”，吃是动作性动词，放在“是...的”句型里，强调吃这个动作的主体。
另外，“被”也可以用在积极的事情中，“他被称为活字典”。