To increase attendance for a flower show, flower shops in the area offered discount coupons to their customers. Show attendance was higher this year, which the organizers attributed to the many discount coupons attendees used. However, the organizers are warned that weather could be a confounding variable in interpreting the rise in attendance. Which statement could explain the effect of confounding?

Because the weather was worse last year, fewer coupons were distributed compared to this year.
Because the weather was similar in both years, it most likely played no role in the attendance increase.
Because coupons were handed out this year and not last year, the weather was different this year compared to last year.
Because the weather was generally better this year compared to last year, the attendance may have increased.