A governments Schedule of Changes in Long-Term Obligations contains an account titled Net Pension Liability. Which of the following events gave rise to this account?

a) The actual plan contribution made by a proprietary fund was less than the annual required contribution determined by an actuary.

b) The actual plan contribution by a governmental fund was less than the annual required contribution determined by an actuary.

c) The actually computed pension liability at year end exceeded the pension plan assets.

d) The actually computed pension liability at year end was less than the pension plan assets.