Answer:
Testimony.
Step-by-step explanation:
Testimony is defined as 'an account of first-hand experience or a solemn affirmation by a witness' which can be the best evidence or proof to substantiate a claim.
In the given speech, the statement made by Leeland exemplifies a 'testimony' which he employs to support his claim i.e. 'need to limit growth at State University.' It would be considered a testimony as it states a 'first-hand experience of a witness('Mary Sue Kaye, Dean of students') who states that there is a lack of availability of enough classes to be offered to students in most majors.' Since it is a first-hand experience by Dean herself, it can be rely upon easily, and therefore, it not only supports the speaker's point but also persuades the audience to believe it.