Stimulation of muscle fibers at a rate of 20 to 40 stimuli per second does not allow for complete relaxation of the fibers before the next stimulatory event. this results in and can lead to incomplete tetany.

Tetanic spasms/ tetanic contractions

Explanation:

Tetanic spasms occurs when a muscle has a sustained contraction because of an increase in action potential in skeletal muscles

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.

a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring.