The correct answer is : mud bricks and animal skin.
The first man made shelters were made of stones and tree branches. After using material such as stone stabs and bones, mud was taken from the ground and dried in the sun to form clay bricks. Mud is a mixture of water and some combinations of soil, silt and clay. Clay is a poor conductor of heat and that is why it was used for isolation as mud houses remain colder in summer and warmer in winter.
Animal skins ( hides ) were also used. They were used as an important source of clothing and shelter for all prehistoric humans. Most of them were used as tents as they were proved to be very durable. Sometimes, they were used as further isolation in houses and pinned upon the bricks, mainly from inside. They also protected the houses from fire.