Taproots consist of one main root whereas, in fibrous roots, the primary root is eliminated. Taproots penetrate deep inside soil whereas fibrous roots are shallow and don't penetrate as deep as taproots. Taproots have monocots. However, taproots have dicots.
The answer to this question is Happiness consists --in--- speaking the truth. The preposition used here is "in". A preposition is a word used to connect things, pronouns, or expressions to different words inside a sentence. They act to associate the general population, articles, time and areas of a sentence.