The correct answer is A, Security A. This is determined by calculating the liquidity duration (LD) for each security, which is a measure of how long it would take to liquidate a position in a security given its average daily trading volume and the fund's holdings. The formula for liquidity duration is:

$LD_i = \frac{Q_i}{(MDV_i \times V_i)}$

where:

• $Q_i$ is the number of shares held in security $i$
• $MDV_i$ is the maximum daily volume allowed for liquidation of security $i$ (expressed as a percentage of average daily volume)
• $V_i$ is the average daily volume of security $i$

The calculations for each security are as follows:

• Security A: $LD_A = \frac{500,000}{(22\% \times 522,000)} = 4.3539$ days
• Security B: $LD_B = \frac{420,000}{(12\% \times 1,328,000)} = 2.6355$ days
• Security C: $LD_C = \frac{256,000}{(18\% \times 710,000)} = 2.0031$ days
• Security D: $LD_D = \frac{640,000}{(20\% \times 848,000)} = 3.7736$ days

Security A has the highest liquidity duration at 4.3539 days, indicating that it would take the longest to liquidate compared to the other securities listed. This is why Security A is the correct answer.