Isometric exercise strengthens muscles without
a.
contracting muscle fibers
b.
changing muscle length
c.
burning calories
d.
conscious effort

B.  changing muscle length

Explanation:

Isometric exercise is a kind of exercise which provides strength to the body. In this exercise the muscle length and angle of the muscle do not change during the process of contraction of muscles during exercise. Several calories  can be burned if the exercise is done with conscious efforts. The isometric exercise is performed in static positions, dynamic range of motions does not occur.

The correct answer is B. Changing the muscle length

Explanation:

Isometric exercise is a type of exercise in which muscle is strengthed through contractions but without the movement of joints or the muscle changing its leg. This occurs because these exercises imply keeping a specific position that represents physical effort but no movement. For example, planks in which you have to lift your own weigh by putting all your weight on your elbows, toes, and forearms is an isometric exercise because it involves contracting your muscles and making an effort but there is no movement and therefore the length of muscles do not change.

the minimum amperage that the current in this wire would have to have so that its weight is completely supported by the magnetic force due to earth's field, assuming that no other forces except gravity act on it