Okay, so the word which was misspelled would be, 'peak'. This is because the spelling of 'peak' relates to a mountain cliff whereas the correct spelling would be 'peek. This is because you are saying that you are checking on the baby. So therefore the last sentence contains the error.
Correct answer is A: The use of words in ads influences future meaning and usage. Semantics is the linguistic and philosophical study of meaning; therefore, the most complete option would be A.