问题如下：
Snow Creek Village West offers its employees a defined benefit pension plan and stock option, Snow Creek Village West complies with US GAAP.
The information on the following table:
Compared to the assumptions Snow used to calculate its periodic pension cost in 2017, earnings in 2018 were higher by the change in the:
选项：
A.discount rate
B.Estimated future salary increases
C.Expected long-term rate of return on plan assets
解释：
B is correct.
考点：养老金的假设
解析：这一题问的是下列哪项变化对2018年的NI增加
A选项：因为pension的maturity通常是很久的，可以类似于债券的duration，此时PBO增长的金额比discount rate减少的金额更大，也就是说PBO增加的影响更大。除非题目特殊说明这个pension要结束了，我们通常认为interest cost是增加的，导致NI降低。
B选项：题目预测2018年的工资增长率下降，那么退休后的工资水平下降，所以每一期摊销的service cost下降，所以NI上升。
C选项Expected long-term rate of return on plan assets的降低，也会使得NI降低的。
future salary是不是既会影响service cost，也会影响PBO呢？因为PBO是退休后cash flow的现值，退休后每年的cash flow是通过future salary乘以一定比例算出来的？
