Identify the structure of the human heart which is a valve between the aorta and the left ventricle of the heart that prevents the blood from flowing back into the left ventricle. (check out the hint)

the circled areas are referred to   as sunspots.   the sunspots are cooler than the   surrounding area.

sunspots are temporary phenomena on the photosphere of the sun that appear visibly as dark spots compared to surrounding regions. they correspond to concentrations of magnetic field flux that inhibit convection and result in reduced surface temperature compared to the surrounding photosphere.

c is the answer. hope this