Which of the following compounds when heated with $CO$ at $150^{\circ}C$ and 500 atm pressure in presence of $BF_3$ forms ethyl propionate?

Question

\[\begin {array} {1 1} (a)\;C_2H_5OH & \quad (b)\;CH_3OCH_3 \\ (c)\;C_2H_5OC_2H_5 & \quad (d)\;CH_3OC_2H_5 \end {array}\]