Swimming alone
Ais never safe, regardless of ability. B. is acceptable in a pool but never in a lake or an ocean. C. increases the benefits of swimming for cardiorespiratory endurance. D. is OK as long as you've been swimming for at least five years.
Ais never safe, regardless of ability. B. is acceptable in a pool but never in a lake or an ocean. C. increases the benefits of swimming for cardiorespiratory endurance. D. is OK as long as you've been swimming for at least five years.