A person who is generous is likely to give a donation to some cause. Thus, the analogy could be read as, “As a generous person is likely to give a donation, so something that is ancillary is likely to provide or give X.” The word “ancillary” comes from the Latin “ancilla,” meaning female servant. In English, something "ancillary" is something that provides secondary support or aid to an operation or undertaking. Thus, among the options provided, “aid” is the best.

Cupidity is an excessive desire for wealth. The word comes from the Latin for “to desire,” from which the name of “Cupid” is likewise derived. Thus, our analogy could be rewritten, “As cupidity is an excessive desire for wealth, so is exhibitionism an excessive desire for X.” An exhibit is a public display of art or any other organized set of items. Exhibitionism is the strong desire to be seen by others (as if to put oneself on exhibit). As such, it is an excessive desire for attention.

Timber is the produced by a sawmill, so the analogy requires a place where iron is produced. The only answer that functions in this manner is “smithy,” which is name for the place that a blacksmith works on metals.

"Hydrogen" and "oxygen" are both elements, whereas a "proton" and an "electron" are both subatomic particles.

"Forest" and "woods" are synonyms, just as "field" and "meadow" mean the same thing.

When water cools, it becomes ice; therefore, this analogy requires that which magma becomes when it cools. Magma is the liquid stone that flows under the earth’s crust. When this cools, it becomes stone again. This is the only option that fits among those provided.

An "aquarium" is designed to contain "fish," just as a "terrarium" is designed to contain "plants."

A sheathe is the covering into which a sword is placed. You have likely seen this in movies that depict knights and warriors. The sheathe is often on the belt of the warrior, and he will place the sword into the sheathe after having used the blade. The analogy could be read, “Just a sheathe is used to cover a sword, so is a veil used to cover a X.” A veil is the covering that is used by women to hide their faces, often for events like weddings. A veil also can be just any type of cloth used to hide something from sight; however, among the options provided, only face stands in relation to veil like sword does to sheathe.

Grain is stored in a silo, so this analogy needs a word that describes a place in which wealth is stored. Abstractly speaking, there are many options for this, for people “store” wealth in stocks, gold, paintings, and many other things. Luckily, none of the answers are tempting in this way, for the others are variously related to wealth but not as places for storage. Only the humble word “bank” fits that usage.

A "trinket" is a small item of little value. The word can describe either jewelry of this type or small items that might be set out as a humble ornament (like a small porcelain statue or something of that sort). Such trinkets can be placed on a shelf, and this makes the most sense among the possible sense of this analogy, given the potential answers. We can say that just as a trinket is placed on a shelf, so too can a tool be placed in a belt. (There are tool belts used by people working with tools.)