"Alluring" is an adjective that means beautiful or attractive. The best choice is "cute," since it means attractive. Considering the other choices, "concerning" means causing worry, "unstable" means constantly changing states of being, "responsible" means able to be relied upon to complete tasks, and "deliberate" means done on purpose or working carefully.

“Serendipitous” means occurring by convenient chance, or "coincidental." As for the other answer choices, “ordained” means having been officially made a member of the clergy, or ordered and decreed; “preordained” means decided beforehand or predestined; “decadent” means degenerate and corrupt or very luxurious; and “demonstrative” means serving to show that something is true or tending to show emotions without reserve.

"Forlorn" means miserable or sad. "Ecstatic" is the antonym; it means extremely happy. "Arrogant" means conceited or full of oneself. "Informed" means having knowledge or information regarding a topic. "Significant" means important or noteworthy.

The word “sensational” does not mean merely able to be seen or something related to being sensed. Instead, it means astonishing and often shocking. When used in the latter sense, it has the connotation of causing scandal or moral judgment. The use of the word for “astonishing” can be seen in a sentence like, “The circus performance was sensational—filled with dangerous lions, fiery pits, and an eight-hundred-foot-long snake.” In the latter sense, one could say, “The crime was so sensational that its details filled the newspaper for three months.”

"Acrimonious" is an adjective that means "angry and bitter" and is used in particular of speech or a debate. So, we need to pick out an adjective that means something like "bitter" and refers to speech. While "well-spoken" might refer to speech, it does not mean "angry and bitter," so it cannot be the correct answer. "Caustic," however, is an adjective that can mean "able to burn or corrode organic tissue by chemical action" or "sarcastic in a scathing and bitter way." Because the second definition of "caustic" is similar to the meaning of "acrimonious," "caustic" is the correct answer.

For something to be described as placid, it means it is calm and tranquil.  For example, someone with a placid disposition is calm and peaceful in nature.

"Demure" is an adjective that means "of a woman or her behavior: reserved, modest, and shy" or "of clothing: lending such an appearance." So, neither "brazen" nor "proud" can be the correct answer because each of those words are an antonym of "demure." Because "shy" is the answer choice closest in meaning to "demure," it is the correct answer.

An ardent statement means that is passionate and very enthusiastic.

"Petulant" and "sullen" both mean crabby or moody. "Guileless" means honest or forthright. "Florid" means very elaborate or decorative. "Extravagant" means indulgent or wasteful. "Esoteric" means mysterious or obscure. 

"Fervent" and "ardent" both mean devout or passionate. "Apathetic" means uncaring or disinterested. "Dispassionate" means unfeeling or impartial. "Intermittent" means irregular or sporadic. "Virulent" means poisonous or lethal.