Quality control chemists in a coal processing plant are conducting a series of experiments on various coal samples. One of the experiments involves burning the coal in order to determine the masses before and after combustion. This coal combustion reaction is shown in the image. At the start of the coal combustion experiment, the mass was 100 grams. At the end of the coal combustion experiment, the mass was 100 grams. During the combustion experiment, heat was transferred from the reaction vessel to the area surrounding the reaction vessel. What type of system was this combustion experiment conducted in?

A. isolated
B. insulated
C. open
D. closed