National goals such as those from Healthy People 2010 and the Centers for Disease Control and Prevention (CDC) encourage curricular goals in school PE that include having students work at moderate to vigorous intensities for at least % of class time.

16.7%

Explanation: Children and adolescents (ages 6 to 17 years) engage in 60 minutes or more of moderate-to-vigorous physical activity daily as described by the CDC in The Physical Activity Guidelines for Americans (second edition).

However, elementary and high schools usually run from 8 a.m to 3 pm (or 3.30pm in some cases) daily. High school students take six one-hour classes or four 90-minute classes and an hour lunch break daily.

Thus, the CDC recommends 60minutes of physical activities daily, which account to 16.7% of the total class duration (6 hours) per day.

answer: land bridge theory. land bridge theory held that shifting portions of dry land explained the finding of identical species on different continents. plate tectonic theory eventually eliminated the land bridge theory.