The Latin prefix somn- means sleep, as in "somnambulist," which means sleepwalker. So, "somnolent" means tired, drowsy, sleepy. "Grumpy" is an adjective used to describe people or behavior that is ill tempered. "Cheerful" is an antonym to "grumpy."

The prefix "pseudo-" means fake or artificial, so it makes sense that a “pseudonym” is a fake name, or an “alias.” A “grievance” is an injustice you feel has been done to you or a problem you might have with something; “fusion” means blend or combination; “diffidence” is lack of self-confidence; and a “prototype” is a first model of something.

The prefix "a-" means without and "chromatic" means having to do with color, so “achromatic” means without color or "colorless." As for the other answer choices, "thoughtless" means inconsiderate and not thinking about others; “colorful” means full of color; “thoughtful” means considerate and kind; “metallic” means made of metal.

To solve this synonym problem you need to rely on your knowledge of Greek prefixes. The prefix ante- means before, so an "antecedent" is something that comes before, also known as a "precursor." To provide further help, a "lamentation" is an expression of mourning; a "frontrunner" is a favorite in a competition; an "outlier" is unusual, outside of the normal reach of data; a "node" is a regional center of human activity. 

The prefix eu- in Greek means good, fine. So the word "euphoria" means a state of feeling very good, deep happiness. 

The Greek prefix hyper- means too much of, so "hyperactive" means having too much energy, restless. Additionally, "cantankerous" means grumpy, bad-tempered; "rambunctious" means playful and boisterous, rowdy; "macabre" means related to death; "susceptible" means vulnerable, likely to be affected by. 

The Greek prefix xer- means dry, so "xeric" means containing very little moisture, dry and arid. "Wet" is an antonym to "xeric."

The Greek prefix icono- means image, as in "iconography" which refers to images used in works of art or traditional settings. So, an "iconoclast" is someone who attacks the image of a treasured institution, a critic, a heretic. Additionally, a "trailblazer" is a pioneer; a "nomad" is someone who wanders from place to place and does not live anywhere; an "itinerant" is a wanderer, a nomad; a "custodian" is a caretaker, someone who looks after something for someone else. 

The Greek prefix crani- means skull, brain, as in "craniology" which is the study of the composition of the skull (it is worth noting that the suffix -ology means study of, as in "biology" or the study of life). So, "cranium" means skull or less commonly brain. Additionally, a "tendon" is a fiber that connects muscle to bone; an "artery" is a vessel that transports blood from the heart to the rest of the body. 

The Greek prefix gyno- means related to women, as in "gynecologist" which is a doctor that specializes in the care of the female body. So, "gynecoid" means relating to women, feminine, qualities associated with women. Additionally, "diligent" means hard-working, rigorous; "masculine" means a quality associated with men; "refined" means dignified, elegant, sophisticated; "juvenile" means childish, immature.