The word “vulnerable” comes from the Latin for wound. With the “-able” prefix, it would mean able to be wounded. Therefore, when someone is “in-vulnerable,” he or she is not able to be wounded. The word “invincible” does not necessarily pertain to wounds, but it does mean unable to be conquered. You may have heard of the famous line attributed to Julius Caesar: “Veni, vidi, vici,” “I came, I saw, I conquered.” The last word, “vici,” is a form of “vincere,” meaning, to conquer. To be “invincible,” is thus to be “un-conquerable.”

The word “exclaim” literally means to shout out. The “ex-” prefix is likely familiar, being taken from the Latin for out or out of. The “-claim” portion is related to words like “clamor” and “proclaim.” It comes from the Latin for to call in the sense of to call out. When someone “exclaims” something, he or she shouts it out, often in anger or surprise. For instance, upon unexpectedly discovering an answer, one might exclaim, “Eureka!”

Ambivalent means being unable to choose between two options. The correct answer choice is undecided.  The prefix "ambi" means both, and the root "val" refers to strength.  

Superfluous means beyond what is needed or an overabundance.  Thus, the correct answer is extra.  The prefix 'super' means over.  

When used as a verb, the word “presage” means to be a sign of a future event, often implying that this is a sign of warning. The word comes from the prefix “pre-”, meaning before, and the base “sage,” which does not merely mean wise, but to perceive keenly. Someone who is “sagacious” is wise precisely because that person keenly perceives reality. The word would be used in a sentence like, “In many cultures, the flying of a crow over a barn presaged a poor harvest in the coming year.”

The word “diffuse” comes from roots that literally mean poured away from. The “di-” prefix means away from or down from, and the “-fuse” means to pour. This latter is found in words like “infuse” (meaning, literally, to pour into) and “effusive” (meaning pouring out, implying that someone “pours out” a great amount of something like praise). As a verb, the word “diffuse” means to scatter or to spread out, as when one diffuses a smell into a room or when an idea diffuses through an entire population. The word can likewise be used as an adjective, basically having the meaning of the past participle of the word, namely “scattered.”

To "preclude" something is to stop it from happening. The prefix "pre-" means before, and the root word, "clud," means to close or to shut. 

"Equivocal" means ambiguous or allowing the possibility of different meanings. The prefix "equi-" means equal.

"Immobile" means incapable of moving or being moved. The root word "mob" means move. The prefix, "im-," means not or without. Thus, the best answer choice is "motionless." 

"Indefatigable" means unable to be tired out. The best choice is "tireless." The prefix "in-" means not, and the Latin root word, "fatigare," means to tire. "Fatigare" is also the root for the word fatigue.