Select the option that expresses the given sentence in passive voice.

I know her.

She is known to me.

In the active voice sentence, "I know her," the subject (I) performs the action (know) on the object (her).

To convert the sentence to passive voice, we make the object (her) the subject of the sentence and use the verb "is known" in the corresponding form. The agent or the doer of the action (I) is introduced with the preposition "to."

Therefore, the passive voice sentence is: "She is known to me."

The other options are incorrect:

1. "She is whom I know" is not in passive voice but rather an active voice sentence where "she" is the subject and "whom I know" is the object. The sentence does not change the focus from the subject to the object, as required in passive voice construction.

2. "She knows me" is also not in passive voice but an active voice sentence where "she" is the subject and "me" is the object. The sentence does not convey the passive voice meaning.

3. "I am known by her" is in passive voice, but it does not match the original sentence structure. In the original sentence, "I" is the subject, but in this option, "I" is the object, and the passive construction does not match.

Therefore, the correct option is: "She is known to me."