Yes indeed, the heart is "cardiac"—the only "cardiac" (associated with the heart) organ in the body. This is not very informative. The same goes for "internal." The sentence clearly wants to set up an opposition between the gallbladder and the heart. You can tell this by the use of the word "although." The gallbladder is not absolutely necessary—you can live without it. The implication is that the heart is necessary. Something is "vital" when it has such necessity, particularly for living. (The word comes from Latin roots related to "life.")

Often, the best approach to a sentence is to try to "fill in the blank" yourself. For this question, consider the fact that the two halves are contrasted. The gadget appeared to be one, single machine. In fact, it actually was "made up" of a number of interrelated ones. The idea is that it was a group of machines, gathered together and interrelated. When you compound things, you mix together (and generally connect) various elements. To "confound" is to cause confusion—don't be confused by this expression of confusion! The other options are likewise quite inappropriate for the purposes of this sentence.

The contrast here is between the types of style under discussion. In the introductory clause, we are discussing Flavia’s ability to write "verse"—poetry. The passage implies that she also had an excellent “non-poetic” style. Prose writing is non-metered writing, and this is the best contrast to “metered verse.” “Writing” is too general, “didactic” means for teaching purposes, and even “essay” does not contrast to “meter” as directly as the word “prose" does.

The contrast in this sentence is between the “simpler and poorer” conditions of the brothers’ childhood and that of Gilbert’s brother today. Indigence and destitution are extreme poverty, so these options are not at all opposite. While stereotypes might tempt us to think of the rich as being "arrogant," we must not go beyond the direct meaning of the sentence. “Posh” describes a luxurious manner of living, and this well contrasts with the brothers’ upbringing.

The contrast in this sentence is between one god and many gods. Our blank is not necessarily about ancient legends. Indeed, it makes little sense to speak of “corporeal” (bodily) stories. The word “deity” means god or god-like being. Words like “deify” (to make into a god) or “theology” (the study of god) are related to “deity.” Therefore, the sentence is speaking of our ancestors believing in many gods—or, many “deities."

The two key descriptors used in this sentence are “exhibit self-motion” and “not found in lifeless beings.” To be “life-filled” and to be “self-moving” is to be “animated.” The word “animated” actually comes from the Latin "anima," meaning soul. We often use the word to describe moving cartoons or perhaps someone who is very active in expressing himself or herself—as in, “He discussed the topic in an animated manner, flailing his hands about in excitement.”

Normally, we use the word “pedestrian” to mean one who is walking instead of driving in a city. The roots of the word would lead us to think this as well, for “pedestrian” is derived from the Latin for “foot,” found in other words like “pedal” and “pedicure;” however, as an adjective, the word can mean “unexciting” or “uninteresting.” Since John is being contrasted with his wife, who has “daring tastes and hobbies,” he must be somewhat unexciting and dull—rather pedestrian.

The contrast in this sentence is between Tilghman’s “svelt” siblings and himself. If someone is “svelt,” he or she is slender; therefore, if he is not svelt, Tilghman must be fat or “corpulent,” which means the same.

The word is derived from an almost identical Latin root that means the same and is more distantly derived from the Latin for “body” found in words like “corpse,” “incorporation,” and “corporeal.”

The sense here is that Frowin occupies a “middle position” between these two, balancing their characteristics. The “mean” of a series of numbers is the average. The term is often used to describe any type of average between two or more things.

The sense of the sentence is that Randall wishes to separate the large dogs from the small ones. The word “segregate” best implies separation of this sort. It literally means “to gather apart (or into parts).”

The prefix “se-” here implies the parts or “apart,” while the “-gregate” is derived from the Latin for “flock,” a root found in “congregation” and “gregarious.”