"Punctual" means prompt or on time. Therefore, "prompt" is the proper synonym. 

"Eternal" means not having an end or lasting forever, so "never-ending" is the correct answer. None of the other answer choices are close in meaning to "eternal": "illiterate" means not having learned to read or write; "jubilant" means extremely happy and joyful; "passive"  means not active; and "pious" means very religious.

"Arbitrary" means unreasonable or undetermined. "Inconsistent" is the best choice because it means contradictory or erratic. When something is "inconsistent," it is constantly changing and therefore cannot be determined. Considering the other choices, "surprised" means shocked or astonished, "jaded" means worn out, and "unruly" means difficult to control.

Something that is "brisk" is best summarized as quick or fast; for example, a "brisk" wind is one that is blustering.  In terms of the other answer choices, "forlorn" means lonely; "steady" means constant; "leisurely" means laidback; and "fierce" means strong or aggressive.

“Constant” means not changing, staying the same. To provide further help, “fallible” means imperfect; “ghastly” means ghost-like or horrific; “contiguous” means sequential; “sustainable” means able to be kept going. 

"Imminent" is defined as likely to occur at any moment, and "impending" is defined as about to happen. These similar definitions make the two words synonyms. 

The word "erratic" means constantly changing or having no certain state. "Irregular" is the best choice because it has a related definition—not regular. Considering the other choices, "true" means accurately reflecting things as they are or correct, "rational" means agreeable to reason, "tacit" means understood without being said, and "flagrant" means brazen or done without care for the obviousness with which one is breaking rules.

"Juvenile” means immature and behaving like a child or young in age, so "childish" is the correct answer. "Variegated" means containing many different colors, especially in a stripe-like pattern; "portentous" means ominous; and "wily" means clever and sneaky.

“Auspicious” means favorable or lucky, so "favorable" is the correct answer. As for the other answer choices, “exuberant” means excited and enthusiastic; “permanent” means lasting or unable to be erased; “transitory” means temporary or not permanent; and “orthodox” means conventional or abiding by a given set of rules.

“Stationary” means unmoving as opposed to in motion, so "unmoving" is the correct answer. As for the other answer choices, “staunch” means committed and firmly supporting; “frosty” means cold; “stern” means strict and sticking to the rules; and "fluid," when used as an adjective, means either flowing or in a liquid form.