A3. $85 \%$ of the students in the final years of the school went on a professional excursion. Which of the following data do you need to calculate how many students in the final years did not go on the professional excursion?

(A) the number of final years

(B) the number of students in the school

(C) the number of students in the final years

(D) the number of supervisors and guides

(E) We do not need additional data.
A3. To calculate the number of students who did not go on the excursion, we need the number of all students in the final years.