A "circumference" is the length of a line that goes around something or that makes a circle or other round shape or the outer edge of a shape or area. We can get this meaning from the prefix "circum-," which usually means around, as in the word "circumnavigate," which means go around something. A "perimeter" is the outside edge of an area or surface, so it is the answer choice closest in meaning to "circumference."

The prefix ab- means away from, as in “absent,” which means not here, or “absolve,” which means to take away blame. In this instance the word “abscond” means to run away. 

The prefix epi- means upon, on top of, and the word “epitaph” means writing upon a tombstone. This is closest in definition to “inscription,” which means writing or a dedication. To provide further help, “comatose” means in a coma-like state; an “individual” is one person.

The prefix mono- means one, and the word “monosyllable” means containing only one syllable. An example of a “monosyllable” sound is a grunt. To provide further help, “proclaim” means formally announce to a large group of people; “badger” means annoy; “dialogue” is conversation between two people. 

The prefix "over-" means too much of, so we know that “overwhelmed” must mean completely taken over or emotionally overcome by something. The word closest in meaning to “overcome” or “taken over” is “inundated.” "Inundated" literally means flooded with water, but can also mean flooded with a great number of something. None of the other answer choices are close in meaning to "overwhelmed": “aloof” means distant; “insipid” means dull; “garrulous” means talkative; and “barrage” means a relentless bombardment.

An “obstacle" is something that gets in the way or an impediment. This makes sense, as "obstacle" contains the prefix "ob," which can mean in the way of. "Impediment" is thus the correct answer. To provide further help, “recalcitrant” means wayward and disobedient; “serendipitous” means owed to chance or good fortune; “unfortunate” means not lucky; and “auspicious” means a favorable beginning that suggests at a good outcome.

The root "trans" in English can mean either go across or to change into a different state. An example of the former would be “transatlantic,” and an example of the latter would be “transform” or “transplant.” To “transplant” means to move to another place or to relocate. It is most commonly heard in English to refer to a surgical procedure where one person’s organs are relocated into another person, usually to save the latter’s life. To provide further help, “administer” means give someone a specific kind and amount of medicine; “portend” means foreshadow or forewarn of something bad; “lament” means mourn; and “imply” means suggest something without directly stating it.

The prefix "ag-" (or "act-") means to make happen, to drive, to move. It can be seen in the words “agent,” which means the reason for making something happen, “action,” and “active.” “Agitate” means to stir up, to incite, to cause people to feel.

The prefix "ego-" means related to the self, related to I. An “egoist” is someone focused on the self or someone focused on the individual. It is closest in meaning to an “individualist.” To provide further help, a “philanthropist” is someone who gives to charity; a “miser” is someone who is stingy with money; “flounder” means struggle; “founder” means person who started a company or organization.

The prefix "mal-" means bad, so “maladjusted” means badly adjusted. When someone is “well-adjusted” it means they are comfortable with themselves and comfortable in society. On the other hand, someone who is “maladjusted” is uncomfortable or unbalanced. To provide further help, “beneficial” means helpful and “benevolent” means good-natured. The prefix "ben-" is often used as an opposite to the prefix "mal-." "Malodorous” means bad-smelling and “unseemly” means gross, unpleasant.