You Are Out Camping in a Remote Region Away from All

You are out camping in a remote region away from all civilization.The next day,you plan to hike around and return to camp before dusk.Your friends suggest that after hiking,you might want to enjoy a warm shower.They suggest that before you head out in the morning,you should suspend a strong,black cloth bag full of about 5 gallons of water,so that it sits in sunshine all day.When you return,the water should be warm,and you can enjoy a luxury because of good planning.It works and you are delighted and refreshed! The process that you used to get a warm shower illustrates

A) passive solar heating.
B) active solar heating.
C) solar space heating.
D) flat-plate collection.