In the following English grammar question, you must choose the most appropriate phrasal verb to complete the sentence meaningfully: One should always set _____ some money aside for emergencies and unexpected expenses.

Introduction / Context:
This question tests your understanding of common English phrasal verbs, specifically those that collocate with the verb "set" to express the idea of reserving or keeping something for a future purpose. In everyday financial planning and spoken English, we often talk about keeping a small amount of money ready for emergencies or unexpected expenses. Choosing the right phrasal verb here shows that you understand both the literal meaning and the idiomatic usage of the phrase in a natural sentence.

Given Data / Assumptions:
- The sentence is: One should always set _____ some money for emergency.- The missing word must combine with "set" to form a correct phrasal verb.- The intended meaning is to reserve or keep money in readiness for emergencies.- The options are: aside, on, by, out.

Concept / Approach:
In English, many verbs form phrasal verbs when combined with prepositions or adverbs such as "up", "out", "aside", and "by". The phrasal verb "set aside" means to reserve or keep something, usually money, time, or resources, for a specific purpose in the future. The other combinations like "set on", "set by", and "set out" have different meanings which do not fit the context of keeping money for emergencies. To answer correctly, you must match the context (saving money) with the phrasal verb whose meaning is "to reserve".

Step-by-Step Solution:
Step 1: Read the sentence carefully and identify the context: saving or reserving money for emergencies.Step 2: Recall the meanings of possible phrasal verbs formed with "set".Step 3: "Set aside" means to keep or reserve something, especially money or time.Step 4: "Set on" usually means to attack or strongly encourage action, which does not fit the idea of saving money.Step 5: "Set by" is rarely used in modern English in this sense and is not the natural collocation here.Step 6: "Set out" means to start a journey or to begin a task, which again does not relate to reserving money.Step 7: Therefore, the only phrasal verb that correctly conveys the meaning is "set aside".

Verification / Alternative check:
As a quick check, you can mentally replace the blank with each option and read the full sentence aloud: "set aside some money", "set on some money", "set by some money", and "set out some money". Only "set aside some money" sounds natural and is commonly used by native speakers when they talk about saving funds for emergencies. This confirms that "aside" is the correct choice in both grammatical and idiomatic terms.

Why Other Options Are Wrong:
Option "on": "Set on some money" is not an accepted phrasal verb for saving money and would confuse the meaning.Option "by": "Set by" is archaic or rare in this context and is not the standard expression in contemporary English.Option "out": "Set out some money" does not mean to reserve funds; it suggests placing something out physically or beginning something.

Common Pitfalls:
Learners sometimes choose a preposition just because it sounds familiar with other verbs, rather than recalling the specific phrasal verb that actually exists in English. Another common error is to think that any preposition can follow "set" and still be accepted, but phrasal verbs are fixed combinations. It is also easy to confuse "set aside" with "put aside", which has the same meaning; however, only "aside" works correctly with "set" in this context. Remember that financial vocabulary often relies on fixed phrases such as "save up", "put by", and "set aside".

Final Answer:
The correct phrasal verb is aside, so the completed sentence is: One should always set aside some money for emergencies and unexpected expenses.