"Extraterrestrial" means alien when used as an adjective, and an "extraterrestrial" is is an alien. So, "alien" is the correct answer. To help you understand the formation of words, consider that "terrestrial" means from the earth and in this context, the prefix "extra-" means something other than. So an extraterrestrial is something from somewhere other than the earth. To help you further, "extraordinary" means something other than ordinary, "ordinary" means normal, a "foreigner" is someone from another country, and a "citizen" is a member of a nation.

If you are “hypersensitive” you are overly sensitive to things. For example, you may easily have your feelings hurt. The prefix "hyper-" usually means overly.

To “surpass” is to go beyond or to become better than someone or something. “Exceed” also means to go beyond the limit of something or to become better than someone or something. Look for prefixes like "sur-" and "ex-" where "sur-" can mean above and "ex-" can mean out of. To further help you, “recede” means to go back, so you can say waves “recede” on the shore.

The prefix "un-" is a negation prefix and usually means not, so the word “unacceptable” means not acceptable. Of the answer choices, this is closest in meaning to “intolerable,” which means not tolerable. The prefix "in-" is used very much like the prefix "un-." To provide further help, “unmitigated” means not mitigated, pure; “domesticity” is life inside the home; “meticulous” means careful, paying great attention to detail; “incomprehensible” means not able to be understood. 

The prefix "under-" means beneath or below, so the word “underage” means below age, immature. To provide further help, a “novice” is a beginner and an “expert” is someone who has been doing something for a long time and is very good at it; a “vendor” is someone who sells things; a “genius” is someone who is very smart. 

“Dismount” means to get down. It is commonly used when speaking about “dismounting" from horses, as in to get off your mount. The prefix "dis-" is a negation prefix and the suffix "-mount" refers to something you sit on.

The prefix "semi-" usually means half, so we can assume that a “semicircle” is half a circle. To provide further help, a three-dimensional circle is called a “sphere;” “parallel” means running alongside, having the same slope; “slope” means slanted ground; “gradient” means slope. In addition to being terms we use in English, these are also all mathematical terms. 

The prefix "under-" means below or beneath, so the word “underdeveloped” means not grown enough, not developed enough. To provide further help, “developed” means grown; “beneath” means under. 

The suffix "-act" means to do, to act, to respond. The word “react” means respond to something. To provide further help, “writhe” means twist in pain; “egress” means exit, way out; “akin” means similar to; “variegated” means different looking, multicolored.

The prefix "over-" means completely, excessively, too much, so the word “overburdened” means carrying too much of a load, or "overloaded.” To provide further help, “overlook” means ignore; “overhead” means above; "overt" means secret.