Why are the answers in the Presidential Schools entrance exams are filled in pencil?

Why are the answers in the Presidential School entrance exams are filled in pencil?

 Writing answers in pencil is one of the requirements of the Cambridge Assessment.
The reason:

▶ Answers filled on a writing instrument other than a pencil are not checked by a special computer. A program that specializes in checking test answers only accepts answers marked in pencil;

▶ The answers marked in pencil are scanned well - when marked with a pen, they are likely to be stained;

▶ Marking the answers in pencil allows the applicant to correct the mistake if he / she makes a mistake.

The same method is used for tests such as IELTS, TOEFL.