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．private property and rights concerned.
B．manpower and natural resources control
C．ownership of productive resources
D．free contracts and prices