Which of the following sentences uses the passive voice? She will write a letter, She is writing a letter, The letter was written by her, She writes a letter

Which of the following sentences uses the passive voice? She will write a letter, She is writing a letter, The letter was written by her, She writes a letter

Explanation

The letter was written by her.

Passive voice emphasizes the action done to the subject.

"Was written by her" clearly shows the passive construction.