The two ways of relating what a person has said are 1)direct and 2)indirect (reported speech).In direct speech, the original speaker's exact words are repeated. In indirect/reported speech, the exact meaning is expressed but not necessarily using the original speaker's exact words. Pronouns and possessive adjectives usually change from first or second person to the third person except when the speaker is reporting his own words. Sometimes a noun can be inserted to avoid doubt.

When we turn direct questions and exclamations into indirect speech, they are converted to affirmative statement .( ? and ! is not used).

Option D is correct as when we convert the request and the reply, we use ' to which'. Also to + infinitive construction is used.  And ok is replaced by in affirmative.

 The other options are wrong as I , is and was she can't be used.

The correct answer is D)Ann requested Ben to lock the door to which Ben replied in affirmative.