We tend to use the word "explosive" to think of things that physically explode—often with very dangerous and fiery consequences; however, think of what explosions are like. They are very sudden things. Quickly, some small item blasts outward—it explodes. Sometimes, we speak of "explosive" things metaphorically, like an "explosive population growth in ducks." This means that the ducks have suddenly had a significant increase in population. Although some of the other options are somehow related to the general notion of explosions, only "sudden" is a proper synonym.

You perhaps have heard the word "lofty" used to describe something that is physically very tall. This is the most obvious and standard meaning of the word; however, this idea of being "high up" can also apply to less material things. For instance, someone can have very "lofty goals" or very "lofty intentions." This means that he or she has chosen a very noble or praiseworthy set of goals or intentions. Such goals or intentions are "above" other goals and intentions in a metaphorical sense.

The most tempting wrong options for this questions are likely "conceal" and "hide." When something is "implicit", it is not completely clear and out in the open. Implicit meanings are things that are not directly stated, though they are "really there." For example, someone might say something like, "Oh yes, it is wonderful that you are here." That person's tone might imply that he or she is actually angry. To imply something, however, is not to hide it. Now, you can also use the word to mean, "involve." It especially can indicate that one thing will be the consequence of something else. Thus, you could say, "The heavy rains imply that there will likely be heavy floods."

The word "healthy" can be used to describe someone's state of physical well-being. It can also just mean "normal" or "enough." For example, you can say that someone has a "healthy appetite." This person has a normal appetite—instead of having one that is sickly and very small. Also, you could say, "He had a healthy suspicion about gambling." This means that the person has a reasonable and normal suspicion about gambling, which is a risk business after all!

"Majority" means more than 50%, or the group with the most members in a given vote or debate. It is the opposite of "minority," which therefore cannot be the correct answer. The right answer is "most," because "most" means more than half. Thus, majority and most are synonyms. While "majority" can sometimes be used as a noun, it can also be used as an adjective. ("The majority of the population" is an example of it being used as a noun, while "the majority vote" is an example of it being used as an adjective.)

"Majority" means more than 50%, or the group with the most members in a given vote or debate. It is the opposite of "minority," which therefore cannot be the correct answer. The right answer is "most," because "most" means more than half. Thus, majority and most are synonyms. While "majority" can sometimes be used as a noun, it can also be used as an adjective. ("The majority of the population" is an example of it being used as a noun, while "the majority vote" is an example of it being used as an adjective.)

Although "regards" has several meanings, one of them is almost interchangeable with "esteem," which means judgement or opinion.

Note that "estimation," a similar-sounding word, is completely unrelated.

Abroad most closely means overseas.  If someone travels or studies abroad, it means they go overseas to another country.

If someone has a hunch, it means they have an idea or feeling about a situation or something in particular.

"Rot" is a verb that means "decay or cause to decay by the action of bacteria and fungi; decompose." While something that is rotting might gross someone out, "gross out" does not mean the same thing as "rot," so it cannot be the correct answer. Because "decay" is the closest synonym to "rot" amongst the listed answer choices, "decay" is the correct answer.