[求助] CFA II - financial-- PBO recognized, allocated, following, discount, expected

Kapie

Mock 30-No.75
75. Which of the following would best support Lee’s concern about the pension
related compensation expense in 2008? The change in the:
A. discount rate.
B. vesting period.
c: Actual return on assets

answer is discount rate.

我的疑问是， compensation expense is base on the fair value of the option on the grant date base on the number of options that are expected to vest, and is allocated in the income statement over the service period.. recognized compensation expense = (total grant option price/ vesting period).
so， 这里这个答案minimized compensation expenses 是否应该是vesting period 阿？