What does the $"10"$ in the $\frac{10}{20}$ Protection ${?}^{TM}$ standard represent?

Select one:

Lifeguards are able to scan their entire assigned zone and recognize a guest in distress within $10$ seconds

The minimum time a guest in distress waits for aid is $10$ seconds

Lifeguards may be distracted for a minimum of $10$ seconds before resuming the scan of their assigned zone

Lifeguards are able to first scan the surface of their assigned zone in $10$ seconds