Answer:
The plate was broken yesterday by my sister.
Step-by-step explanation:
To make a sentence passive from active, change the verbal wording choice and put in a preposition plus, make the original subject (person/place/thing) the object and the object the subject.
In this case, the sister is the subject and the plate is the object.
When we change this sentence, we make the sister the object and the plate the subject. To do this we first say the object (in this circumstance the plate), then put the subject in the end.
My sister broke a plate yesterday.
Becomes:
The plate ____ my sister yesterday.
Now, we have to make the verb a past participle.
Broke becomes was broken.
Then, put a preposition (by) to show that the subject is the object.
The plate was broken by my sister yesterday.