The correct option is C c
Let’s examine the sentence: “The taxi came at 8 o'clock in the next morning.” The sentence uses the preposition “in” after the time given in the “o’clock” style. This is wrong as “o’clock” style of time does not require any preposition after it. So, the sentence needs to drop “in” to correct itself. So, the error is in Part c of the sentence. Hence, Option C is the correct answer.