In this English vocabulary question, choose the option that is closest in meaning to the word curtail, which is often used in formal writing and governance contexts.

Introduction / Context:
Vocabulary questions commonly test your ability to recognise synonyms, that is, words with similar meanings. The word curtail appears often in newspapers, policy discussions, and academic writing. It generally refers to reducing, cutting short, or limiting something, such as curtailing expenses, curtailing freedom, or curtailing production. To answer this type of question correctly you must connect the target word with the correct semantic idea and identify the option that best matches that idea in normal English usage.

Given Data / Assumptions:

• The word given is curtail.
• The options are: Prolong, Downsize, Lengthen, Extend.
• Only one option must be the closest in meaning, while the others serve as distractors.
• The question is from a general English section for competitive exams.

Concept / Approach:
Curtail means to reduce, cut down, or place a limit on something. It implies making something smaller in amount, duration, or extent. Therefore, we need a word that also carries the idea of reduction. Among the given choices, downsize is commonly used to describe reducing the size of an organisation, staff, or operation, and therefore it reflects the idea of shrinking or cutting down. The remaining options all imply increase or extension of time or size, which is the opposite of what curtail means.

Step-by-Step Solution:
Step 1: Recall or deduce the meaning of curtail from context you may have seen earlier such as curtail expenses or curtail rights.Step 2: Restate this meaning in your own words as reduce, limit, or cut short.Step 3: Compare each option with this restated meaning.Step 4: Prolong means to make something last longer, which is the opposite of cutting short.Step 5: Downsize means to reduce in number, size, or scale, especially with regard to jobs or a company, which aligns well with the meaning of curtail.Step 6: Lengthen means to make longer and extend means to stretch or increase duration, so both contradict the idea of reduction.

Verification / Alternative Check:
To verify, try placing the synonyms in typical sentences. If a company decides to curtail its workforce, it is reducing staff strength. If a company decides to downsize its workforce, the meaning is practically the same. If you replace curtail with prolong, lengthen, or extend, the sentences start meaning the opposite. This simple test of substitution confirms that downsize is the only valid synonym among the options given in this exam question.

Why Other Options Are Wrong:
Prolong means to make something last longer in time, which directly conflicts with the idea of cutting short. Lengthen also means to increase length or duration. Extend means to stretch or continue something further in space or time. All three imply an increase rather than a reduction. They are therefore antonyms or near antonyms of curtail and cannot be chosen as words similar in meaning in this context.

Common Pitfalls:
A common mistake is to confuse curtail with any formal sounding word without checking the actual sense. Another error is to rush and mark extend because it appears frequently in formal writing. Some learners also mix up downsize and resize, assuming that downsize is too specific to companies. Although it is often used for organisations, it still fundamentally means to reduce size, which matches the core idea of curtail very well. Always focus on the central concept of the target word, not the narrow context in which you have seen it before.

Final Answer:
The correct answer is Downsize.