The correct word for sentence 1) is C) invariably.
"Invariably" means always or on every occasion. It is the correct option because "invariably" is an adverb and it is modifying the adjective "possessed". Furthermore, options A), B) and D) are incorrect because "variability", "invariability" and "variance" are nouns and they cannot follow the verb nor modify the adjective "possessed" in this sentence.
The correct word for sentence 2) is C) gullible.
The word "gullible" refers to someone that is easily fooled or cheated. It is the correct option because "gullible" is an adjective that is modifying the noun "recruit", in other words, the adjective is describing the recruit. Furthermore, option A) is incorrect because "gullibility" is a noun and; therefore, it could not describe the noun "recruit". Moreover, option B) is also incorrect because the word "gullibly" does not exist. The correct way of spelling the word is "gullible".