The passage is a piece of______.

A．wearing appropriate clothing and shoes
B．being mentally ready for physical exercises
C．including periods of warm -up and cool- down
D．avoiding any pressure to their hearts

A．older adults need more physical exercises than the younger ones
B．younger adults are not necessary to take a physical examination before a fitness program
C．fitness programs for older adults should be well -monitored
D．poorly - designed fitness programs for older adults will do serious harms to them