The word "substantial" can mean that something is not ideal but instead is real and tangible. (Something "tangible" can be touched. This is related to the word "tactile.") In contrast to something substantial, the word "intangible"—not touchable—is an excellent antonym.

When something is "opaque," that thing prevents light from passing through it. For example, a house wall is opaque to the light in a given room, preventing it from passing into the next room. In contrast to this, the windows in the room are "translucent," meaning that they allow light through them. This word comes from the combination of the prefix "trans-," meaning across, and "lucent," which comes from light. Translucent surfaces literally allow light to shine through or across them.

"Placid" is an adjective that can mean calm; not easily excited when talking about a living organism. It can also mean calm when describing water. When taking a test, if there is more than one meaning for a word, it is best to look at all of the possible answers and eliminate the ones that don't fit any definition.

Using this strategy, we can eliminate "tranquil," because it means peaceful. This is a synonym of "placid," not an antonym.

"Perplexed" can also be eliminated because it means confused. This is not the opposite of "calm."

"Innocent" means harmless and free of guilt. Again, this is not the opposite of calm.

This leaves us with two possibilities: "excitable" and "aggravating." "Excitable" is an adjective meaning easily excited. "Aggravating" is an adjective meaning irritating. "Excitable" is the best antonym for the first definition of "placid."

Most of the wrong answers are trying to make you think that the "ver-" at the beginning of "veracious" is the same as "very." However, this comes from the Latin for truth. Someone is called "veracious" when he or she is truthful. (Likewise, words are called "veracious" when they are truthful.) The best contrast to this is "deceitful," which is quite opposed to being truthful.

When something is authentic, it is accepted as being genuine—not judged as being a fake version of something. Sometimes, people will speak of a person as being "authentic," implying that he or she is not fake in his or her self-presentation; however, for this question, the general sense is "authentic" as genuine. A forgery is far from being a genuine version—it is a faked version meant to trick people. (Think of a forged signature.)

The word "nascent" comes from roots similar to those of "natal" and "nativity." These words all have to do with birth or coming to birth. Here, the sense is of something that is coming into existence—a nascent idea or a nascent personality trait (or something else of the like). In contrast to this, something dying is ending its time of existence and development.

"Illiterate" means not literate or able to read. Since literacy is a basic part of education, an illiterate person is almost certain to be uneducated. None of the other words are relevant to the idea of literacy.

We create a monument to remember some kind of great event or person. When something is described as being "monumental," that thing is being noted for its importance. In contrast to this, "trifling" means trivial or unimportant. "Trifles" are small and unimportant matters.

When something is trite, it is overused or repeated to the point of being of little worth or help. For instance, a trite expression is one that is so common that everyone knows it; therefore, it helps very little even to repeat it. In contrast to this, something that is "consequential" is important—as though it were something "having great consequences".

The adjective "elementary" means simple or pertaining to the elements (i.e. the basic parts). We call the first stage of education "elementary school" because it represents the place where beginning concepts are taught. In contrast to such simple matters, an "intricate" problem or affair is something that is complex and difficult.