What does the word "chronic" (Sentence 3) mean

A．a slowing of the body's curative processes
B．a collapse of the autonomic nervous system
C．an emotional state that ranges from extremes of depression to happiness
D．an evident and gradual decrease in the physical symptoms of the disease

A．risking harm to their patients
B．prolonging their patients' agonies
C．curing over 50 percent of serious diseases
D．helping their patients psychologically