The pronoun "who" should be replaced with "whom" in the following sentences:
- The water from the faucet has turned brown, but I'm not sure whom to call about it.
- Who do you think should be the next president of the science club?
(Note that the second example is a question where "who" is correct in this structure; you might be looking for something specific here but typically would only change "who" to "whom" in the case of a preposition or an object position.)
In this case, the only clear instance requiring change is the first sentence. Thank you for your patience, and let me know if you need further assistance!