Which of the following compound is expected to have maximum enol content in ethanol?

Question

$\begin{array}{1 1}(a)\;CH_3COCH_2COCH_3\\(b)\;CH_3COCH_2CO_2C_2H_5\\(c)\;CH_3COCHCH_3COCH_3\\(d)\;All\end{array}$