Which interrogative pronoun should replace the blank space in the following sentence?: ___ did you tell?
It is "Whom did you tell?"
It might not sound correct but if you rewrote the sentence as "To whom did you tell my secret?" then it sounds better.
If you are confused between 'who' and 'whom' use this hack.
he = who/ she=who
him = whom/ her=whom
For example, if you were to answer the question, "Whom did you tell?" you can't say "I told he", you would say "I told him". Therefore, you know it's whom and not who.
Another example is, "___ wrote the letter?".
If you answer this question you can't say, "Her wrote the letter", you would say "She wrote the letter." Therefore you know it's who and not whom.