Concept:A question tag must match the main statement in tense, pronoun, and polarity (positive statement → negative tag, and vice versa).
Explanation:The main clause "You will come" is positive and uses the pronoun "you" and future tense "will".
Therefore, the tag must be negative and use the same pronoun and auxiliary verb: "won't you?".
The given tag "isn't it?" does not match the pronoun "you" or the tense.
For example: "They have eaten, haven't they?" not "isn't it?".
So the error is in part c).
Answer:C