The author mentions that the maximum THR for older adult participants in sports should he less than ______ beats per minute.

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

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