Answer:
The law of conservation of mass
Explanation:
The Law of Conservation of Mass dates from Antoine Lavoisier's 1789 discovery that mass is neither created nor destroyed in chemical reactions. In other words, the mass of any one element at the beginning of a reaction will equal the mass of that element at the end of the reaction.
They determine the north and south ends
Make/produce and secrete hormones
One should consider: proper clothing and shoes-so not to get injured. Knowledge of equipment and activity—one should know how to use all equipment and know how to play the games/activity so not to hurt themselves or others. Proper hydration and nutrition before hand-so not to get dehydrated or dizzy or sick and safety og equipment and location-check for broken items and discard, check environment for hills, holes, sticks, traffic, etc.