Explanation

Part (b), 'since', is the error. 'Since' is used with a point in time, as in 'since Monday' or 'since 2020', whereas 'for' is used with a period or duration of time. 'Two days' is a duration, so the correct preposition is 'for'. The present perfect 'have not had' correctly combines with 'for two days' to show a state continuing up to the present. Option (B) is therefore correct.