Bottle A is filled with air, and Bottle B is filled with carbon dioxide of equal temperatures. Each bottle is placed 50 cm from a heat source, and the temperature inside each bottle is recorded every 5 minutes. Which statement describes the results of the experiment after an hour?

a. The temperatures in the bottles increased equally.
b. Bottle B has a higher temperature than Bottle A.
c. Bottle A has a higher temperature than Bottle B.
d. The temperature of neither bottle increased.