Assume that most of the investors in the stock market are active in an online chat group. As one of the investors holding ABC shares, you find out that the ABC stock has an expected return of $9\mathrm{.}8\%$ from the perspective of most investors in the chat group. In addition, you gathered the following information by carrying out market research. In your research, the market return is $6\mathrm{.}8\%$ and the risk$-$free rate is estimated to be $3\%.$ The beta and past $1-$month variance of Stock ABC is $1\mathrm{.}2$ and $7\mathrm{.}8\%$ respectively. The stock price exhibits an upward trend last week.

Should you buy or sell Stock ABC if CAPM is correct? Why?