Which conditions best describe a zone that is the appropriate size? A lifeguard can see everyone who is on the surface.
A lifeguard can scan the entire zone in 20 seconds and can scan to the farthest point in 10 seconds.
A lifeguard can count the number of people in the zone.
A lifeguard can scan the entire zone in 10 seconds and can get to the farthest point in 20 seconds.