Static stretching refers to
a-stretching that involves bobbing or j. e.r. k.i. n.g motion using momentum
b-stretching in a continuous slow controlled manner
c- a form of stretching in which the body is pushed beyond the initial limit
d-slowly stretching to the to the farthest point without pain

Static stretching refers to stretching which encourages you to slowly stretch your body to the farthest point without pain (but it can also hurt a bit, it just has to stay under the limit of discomfort) and you have to keep it in that position for some time. For that reason, I'd say that the correct answer is D. 

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