According to the passage, "chemistry" (para 5, line 2) means ______.

A．Diet is the most important factor for reducing obesity.
B．Physical exercise is important for reducing obesity.
C．Keeping a good mood is essential for reducing obesity.
D．Going to the gym is key for reducing obesity.

A．one should exercise 30 minutes a week
B．one should try different activities everyday
C．one should exercise moderately on a regular basis
D．one should avoid smoking