A. upright
B. taut
C. uneven
D. tough
Flaccid : (of part of the body) soft and hanging loosely or limply, especially so as to look or feel unpleasant.
Upright : (of a person) sitting or standing with the back straight.
Taut : stretched or pulled tight; not slack.
Uneven : not level or smooth.
Tough : (of a substance or object) strong enough to withstand adverse conditions or rough handling.
Antonym of Flaccid is Taut
