The "Lockup" Problem Involved in Rebalancing Refers to The

The "lockup" problem involved in rebalancing refers to the:

A) problem that investors face in retirement accounts that cannot be liquidated prior to retirement.
B) trust accounts that are not managed by the investor and cannot be traded without incurring administrative costs.
C) taxable accounts subject to capital gains taxes if investments are traded.
D) problem of fixed-income securities that have little liquidity and therefore,must be held till maturity.