Rico and chris are close friends and classmates. each day they are an important influence on each other's actions. this example best demonstrates their:

this null effect is caused by a weak manipulation and ineffective internal validity. in a scientific study, as the one dr. morimoto is trying to perfom, internal validity refers to the confidence placed in the cause-effect relationship and to how well an experiment is done and able to eliminate confounding variables.        

the correct answer is "hematoma formation, with ligaments that are stretched, partially, of fully torn" ankle sprain are produced by an injury to the tough bands of tissue (ligaments) that surround and connect the bones of the leg to the foot. this causes several damage to the ankle including hematoma formation and ligament injury .