I. Read the text carefully and then fill out the missing information in the following short passage. The beginning letter of each missing word has been given. In the human body,muscles are essential elements which 1 c chemical energy into 2 m work. The forces thus 3 g move limbs, 4 i the lungs,pump blood,close and open tubes,etc. Muscle tissue 5 c 40-50% of the body masss. Myocytes 6 d along one of the three main pathways to form 7 s , c ardiac , or smooth muscles. The 8 b of the wall of the heart is 9 c of cardiac muscles . Like skeletal muscle,it is striated in appearance. Unlike skeletal muscle, its contraction is usually involuntary (not under 10 c control). Smooth muscle is found in all systems of the body, in the walls of the viscera except the heart. It appears untriated(smooth) and is also under 11 i control. Named for its location, skeletal muscle is 12 a to the skeleton. It is sometimes referred to as voluntary muscle,because it is often made to contract or relax by conscious control.