"Arid" is an adjective that means "having little or no rain; too dry or barren to support vegetation" when it refers to land or climate, or "lacking in interest, excitement, or meaning" in referring to other things. So, we need to pick out an answer choice that means something like either "dry" or "boring." While "airy" may look like a potentially correct answer choice because it is similar in spelling and pronunciation to "arid," "airy" does not mean "dry" or "boring," so it cannot be the correct answer. "Dry" is the answer choice closest in meaning to "arid," so it is the correct answer.

Something that is "appetizing" is something that makes one want to eat. The answer choice closest in meaning to "appetizing" is "tempting," which means enticing or appealing, even though enjoying it might be a bad idea or wrong, so "tempting" is the correct answer.

"Delectable" means tasty or delicious, so "tasty" is the correct answer. To help you, "circumstantial" means accidental or owed to circumstance, "outrageous" means ridiculous, "ubiquitous" means ever-present or everywhere, and "surrogate" means substitute, stand-in, or replacement.

"Combustible" means explosive, while "volatile" means liable to change or explode. Thus, "combustible" is closest in meaning to "volatile."

Someone or something that is "robust" is strong and sturdy, so "strong" is the correct answer. To help you, "timid," "shy," and "introverted" are all loose synonyms of one another. Someone who is "timid" is shy and weak, and someone who is "introverted" is shy, reserved, and quiet.

"Pallid" means pale in appearance, often due to being sick. "Pale" means lacking vibrancy of color. Therefore, "pale" is closest in meaning to the word "pallid." While pallid people are sometimes weak because they are sometimes sick, "weak" does not have the same meaning as "pallid," and so it is a tempting wrong answer. "Pigmented" means having color as opposed to not having color, which is the opposite of "pallid."

"Luminous" means bright and shining. The best choice is "bright" as it is a part of the definition of "luminous." 

The word "mellifluous" means sweetly flowing or sounding. The best choice is "dulcet," which also means sweetly sounding. Considering the other choices, "flulike" means resembling symptoms of the flu, "melted" means having become liquid, and "enraged" means angry.

Something that is "ductile" is very malleable, easily shaped into something different, or easily influenced. So, for example, clay is ductile. So, "malleable" is the correct answer. None of the other answer choices are close in meaning to "ductile": "despicable" means wicked; an animal that is "nocturnal" is awake at night and asleep during the day; "visible" means able to be seen; and "sensible" means proper, considerate, or not foolish.

Something that is "durable" is long-lasting and thus, the best fit is "indestructible" which indicates something that is unable to be broken or damaged easily. "Impermanent" means lasting only for a short amount of time; "dainty" means fragile; and "flimsy" means delicate.