Perspicuous means clearly expressed and easily understood, lucid.
Option B is the correct answer because “lucid” means something that is expressed clearly hence it Ian the correct answer.
Option A is incorrect because “synthetic” means artificial or man made, hence incorrect.
Option C is incorrect because ineffective means something that doesn’t show the desired result that was aimed at, not related to the given word.
Option D Is incorrect because to obscure means to hide which Ian not related to the given word.