The strongest muscle contractions are normally achieved by

a) increasing the stimulation up to the maximal stimulus
b) increasing stimulus above the threshold
c) increasing stimulus above the treppe stimulus
d) recruiting small and medium muscle fibers

a) increasing the stimulation up to the maximal stimulus

Explanation:

The strength of a muscle contraction is determined by:

Level of motor unit recruitment: the size and number of motor neurons being stimulated in a particular muscle. Muscle cross-sectional area: The greater the cross-sectional area of the muscle, the more muscle fibres that can be activated simultaneously. Muscle stretch: A muscle fibre can shorten to about 50 % to 60 % of its length, but it will be less efficient if it is already short.That’s why many athletes use a brief dynamic stretch sequence as a warm-up prior to their strength work.

Number 1 is the only necessary factor for your answer.