Correct Option: C

opaque (Adjective) : not clear enough to see through or allow light through ; not clean ; difficult to understand ; impenetrable
transparent (Adjective) : allowing you to see through something; obvious ; easy to understand
clear (Adjective) : easy to understand ; obvious ; having or feeling no doubt of confusion ; thinking in a sensible and logical way, easy to see/hear ; transparent
ambiguity (Noun) : the state of having more than one meaning ; the state of being difficult to understand
crystal (Noun) : a small piece of substance with many even sides, that is formed naturally when the substance becomes solid