To improve cardiorespiratory endurance, activities that use most of the large-muscle groups of the body and elevate heart rate should be sustained for at least . a. 40 minutes b. 2 hours c. 1½ hours d. 1 hour e. 20 minutes

E. 20 minutes

Explanation:

Cardiorespiratory endurance is achieved by exercise. The exercise increases the heart beat and decreases cardiovascular disease.Aerobic exercises and activities such as cycling, swimming and running is preferable. The exercise should be done 3-5 times a day for 20-60 minutes for the desired result.

step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.