Isometric exercises strengthen muscles without moving the muscles. Isometric exercises tense muscles but do not change the angle of the joint or cause the muscle to lengthen or contract like normal exercises do. These exercises usually consist of "holding" a certain position in which some muscle or muscles are tensed. A prime example of such an exercise is the plank. A.
contracting muscle fibers
B.
changing muscle length
C.
burning calories
D.
conscious effort

A.  contracting muscle fibers.

C.  burning calories

Explanation:

Isometric exercises are the exercises which cause the contraction of muscles only but not to change the length and joint of the muscles. It builds and maintain strength of the body and also helps in burning of calories as a result loosing of weight occur. This exercise burns about two to five calories per minute and boost your metabolism which leads to lower weight.

the answer is a a teenager needs more sleep than the adult no matter what

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