"Unexpected" is an adjective that means not expected. So, the answer choice closest in meaning to "unexpected" is "surprising," an adjective that means unexpected. None of the other answers are close in meaning to "unexpected": "gradual" means slowly taking place; "bold" means confident and courageous; and "brash" means assertive in a rude way.

"Destructive" means causing damage. Ruinous also means disastrous or causing damage, so "ruinous" is the correct answer. As for the other answer choices, "considerable" means noticeable due to large size or amount, "brief" means short or quick, a "frontier" is a border between two countries, and to "boast" means to talk about yourself and your achievements with pride.

"Damaging" means harmful or causing damage. To further help you, "considerate" means thoughtful about other people’s feelings; "inconsiderate" means unkind and not caring; "applicable" means able to be applied to or relevant. 

When we say that something is "in peril" or "imperiled," that thing is in a state of great danger or risk. The word "perilous" is the adjective that describes such a state ("a perilous situation"). Perilous situations are likely to be very frightening or even terrifying. However, these words really indicate what perilous things emotionally cause. They do not describe what it is to be perilous. "To be perilous" means to be very dangerous. Therefore, the best option is "hazardous." A "hazard" is a danger or a source of danger. "Hazardous" describes something that is dangerous.

The word "fatal" is related to the word "fate," which indicates the idea that something is meant to happen. However, "fatal" indicates a particular kind of "fated" occurrence, namely death. Things that happen by "fate" often are ominous or threatening. A "fatal" wound is one that is likely to kill. Therefore, the best synonyms will reflect either complete destruction or the causing of death. While something that is fatal might be depressing, something that is depressing really is not deadly (at least, not necessarily). The two words describe two different things. The best option is "deadly," meaning likely to kill.

When we "prohibit" something, we ban it or forbid it from being done. "Prohibited substances" are things that cannot be taken into a given area. For example, beer is often a prohibited substance in gaming arenas, meaning that you are not permitted to take it into such areas. The best option among those given is "forbidden," which indicates such banning. Although someone can be condemned for having such a prohibited thing, that is not what is indicated by the word "prohibition" itself. Likewise, a prohibited substance might be "dangerous." This does not mean the same thing as "prohibited" itself.

Bungled means failed or messed-up. To further help you, appropriate means right for the moment, good; inappropriate means not proper, bad.

"Painstaking" means accomplished with care and attention to detail. "Careful" is therefore the word that most closely matches the definition. "Painful" is a tempting choice, but the word "painstaking" actually has little to do with physical pain. "Reckless" is the opposite of "painstaking," and "malicious," which means intentionally causing harm, is unrelated to the definition.  

Estranged refers to a person, often a family member, who is no longer close with another person, or alienated from him/her; therefore, "distant" is the best answer.

Diligent, which is often used to describe someone as hardworking, also means displaying care or being dutiful in one's work. "Conscientious" means the same thing, someone who works well and thoroughly.