Out of those ones, im sure its c. It's definitely not b or d. It allows motion but also protects vital organs. :)
Universal pH paper turns red if it is very strongly acidic, turns orange if it is strongly acidic, turns yellow if it is weakly acidic, green if it is weakly alkali and blue if it is strongly alkali.
Solution A will turn orange as it is strongly acidic
Solution B will turn blue as it is strongly alkali
Solution C will turn yellowish green as it is neutral
Feet would be the best unit to use. Yards would work as well though.
Hope that helps!
