If something is benign such as the weather, it indicates that it is mild.  In the case of weather, benign conditions are the opposite of inclement weather.

"Wretched" and "deplorable" both mean terrible or miserable. "Reassuring" means bolstering or cheerful. "Willful" means stubborn or obstinate. "Wary" means careful or cautious. "Queasy" means uncomfortable or fidgety.

"Shabby" means run-down or in worn-out condition. "Tactful" means acting with skill and delicacy in dealing with other people's issues. "Essential" means required or very important. "Jubilant" means very happy and joyful. "Miniature" means a smaller version.

The definition of "mundane" is everyday or ordinary, making "common" the only possible choice.

The word “prodigious” is related to the same root word as “prodigy,” which is often used to describe a person who has great skills. For instance, many people talked of Mozart as a “child prodigy” because he could play the piano with great skill at a young age. When something is “prodigious,” it is impressive, magnificent, or at least grand in scope or degree. Among the options provided, “monumental” best captures this sense.

When something "meanders" it moves in a way that is not direct but, instead, zigzags from one point to another. Now, this can be used to describe physical motion ("meandering in the fields"). It can also be used to describe something physical and motionless, like a path that zigzags and thus is said to "meander." Finally, it can be used to describe things like thought processes.  Someone's "meandering thoughts" circle about, considering different things for some time before finally resting in a conclusion. Thus, the word "circuitous" works well as a synonym. This word comes from roots meaning circle or around. "Circuitous" reasoning is a kind of thinking that takes a much longer time to arrive at its end than is strictly necessary. A circuitous path is one that meanders quite a bit before reaching its destination. 

The word "minuscule" is related to very familiar words like "miniature" and the often-used prefix "mini-". This cluster of words generally designates that a given things is small.  Something that is "minuscule" is very small or tiny. Hence, the best option among those provided is "microscopic." The options "shrunken" or "short" do not express the tininess involved in being "minuscule."

When something is "engrossing," it is very interesting, drawing someone's attention completely. It comes from roots that are related to the word "gross" that describes twelve dozen of something. To be "engrossed" is to be entirely taken in an interested by something. Thus, the only appropriate option among those offered here is "engaging."

The word "vague" comes from the same root that we find in "vagabond," which describes a person who wanders around. (Likewise, there is "vagrant", which has a similar meaning.) Something that is "vague" is not clear—as though it "wanders around" clarity but never actually settles on a single meaning or appearance. Among the options given here, the only one that describes such a state of imprecision is "indefinite." Something that is "in-definite" is not well defined or certain. It is hazy and thus "vague."

When something is "arduous" it is difficult, thus requiring a lot of work and effort to be completed. Thus, if we were to say, "The yardwork was an arduous affair", we would mean by this that it was very difficult to complete. Do not confuse this with "ardor," which indicates enthusiasm. These come from different Latin roots.  "Arduous" comes from "difficult," while "ardor" comes from "to burn." The best option for this question is "strenuous". Think of this as meaning, "Requiring a lot of straining (i.e. a lot of difficult work)."