The correct answer is that only Stock X should be included in the portfolio. This is because Stock X exhibits the highest liquidity among the four options. Liquidity in the stock market is determined by the ease with which a stock can be bought or sold without causing a significant change in its price. One of the key indicators of a stock's liquidity is the bid-ask spread, which is the difference between the highest price that a buyer is willing to pay for a stock (the bid) and the lowest price at which a seller is willing to sell a stock (the ask). A smaller bid-ask spread indicates higher liquidity because it means that the stock can be bought or sold at a price close to the market price. In the case of Stock X, the bid-ask spread is very small ($12.32 - $12.30 = $0.02), indicating high liquidity. Therefore, Stock X meets the requirement stipulated in the fund's investment policy statement and should be included in the portfolio.

Choice A is incorrect. While stock X is a viable option due to its narrow bid-ask spread indicating high liquidity, stock Y is not a good choice. The majority of the shares are held by a single family and the daily turnover is very low, which suggests that the stock may not be easily tradable and hence lacks liquidity.

Choice C is incorrect. As explained above, Stock Y has low liquidity due to concentrated ownership and low daily turnover.

Choice D is incorrect. Although Stock X can be included in the portfolio due to its high liquidity, Stock A should not be considered because of its wide bid-ask spread ($4.65-$8.25), which indicates lower liquidity.