In English grammar, there are certain rules about when to use capital letters.
All sentences must always begin with a capital letter to mark the start of a new thought.
Names of people, places, days, and months are considered proper nouns and their first letter is always capitalized.
For example: January, February, Monday, London, John.
Option (C) says that the first letter in the names of all months is with a small letter, which is incorrect because month names must always start with a capital letter.
Option (D) is correct because the pronoun ‘I’ is always capitalized when used alone.
Therefore, option (C) is the only incorrect statement.