The Capital Asset Pricing Model (CAPM) is a financial model that determines the expected return of an asset based on its beta and expected market returns. In this case, the beta of ABC Corporation's stock is 0.69, which means that the stock's return is 69% as volatile as the market's return. The remaining 31% of the return is not explained by the market's return, and can be considered as the risk-free rate. Therefore, a portfolio that consists of 31% T-Bills (which are considered risk-free) and 69% of the market portfolio would mimic the returns of ABC Corporation's stock. This is because the return of the portfolio would be 31% of the risk-free rate (from the T-Bills) plus 69% of the market return, which is the same as the return of ABC Corporation's stock according to the CAPM model.

Choice A is incorrect. This choice suggests a portfolio composition of 25% T-Bills and 75% of the market portfolio. However, this does not align with the beta coefficient from the regression analysis which is 0.69. The beta coefficient indicates that ABC Corporation's stock has a lower sensitivity to market movements than what this choice suggests.

Choice B is incorrect. This option proposes a portfolio composition of 35% T-Bills and 65% of the market portfolio, which again does not match with the beta value from our regression analysis (0.69). The proportion invested in the market portfolio should be equal to ABC Corporation's stock's sensitivity to market movements, as indicated by its beta.

Choice D is incorrect. As explained above, this option also fails to replicate ABC Corporation's returns because it suggests investing 33% in T-Bills and 67% in the market portfolio - proportions that do not align with our calculated beta value (0.69).