In the following question, out of the given four alternatives, select the one which best expresses the meaning of the given word. Curtail.

Introduction / Context:
This vocabulary question asks for a synonym of the verb curtail. Such questions test whether you know both the meaning and the direction of common verbs. Curtail is often used in formal writing about budgets, freedoms, programmes or activities that are reduced or cut short. You must select the option that is closest in meaning to this idea of reducing or cutting down.

Given Data / Assumptions:

• Target word: Curtail.
• Options: Prolong, Downsize, Lengthen, Extend.
• The word appears without additional context, but its usual meanings apply.

Concept / Approach:
Curtail means to reduce in quantity, extent or duration, or to cut short something that was planned or in progress. It has a negative or limiting sense. Among the options, downsize means to reduce size, scale or number, especially in organisations or projects, and is closest to curtail in overall meaning. The other three options all mean to increase duration or amount in some way: prolong means to make longer in time, lengthen to make longer in distance or time, and extend to stretch out or increase. These are opposite in direction to curtail.

Step-by-Step Solution:
Step 1: Recall the main meaning of curtail: to cut down, reduce or shorten.Step 2: Consider typical phrases such as curtail spending, curtail freedom, curtail the programme, all of which involve limiting something.Step 3: Examine downsize, which describes reducing size or capacity, especially in companies or plans.Step 4: See that both curtail and downsize involve cutting back or reducing, making them close synonyms.Step 5: Note that prolong, lengthen and extend all involve making something last longer or become larger.Step 6: Choose downsize as the only option that shares the same basic direction of change as curtail.

Verification / Alternative check:
Use the words in similar example sentences. If the company decides to curtail its operations, it might close some branches. If the company decides to downsize its operations, it might also close some branches. The overall effect is similar: a reduction in scale. By contrast, if the company decides to extend or prolong its operations, it would keep working longer or on a larger scale, which is the opposite of curtail. This comparison confirms that downsize is the best synonym from the list.

Why Other Options Are Wrong:
Prolong: This means to make something continue for a longer time, as in prolong the meeting or prolong the conflict, which goes against the idea of cutting something short. Lengthen: This is used to mean make longer, often for objects or time, such as lengthen a skirt or lengthen a deadline. This is again the reverse of reducing. Extend: Extend means to stretch out or make greater in area, distance or time, as in extend the road, extend support, or extend the contract. It does not carry the idea of reduction.

Common Pitfalls:
Sometimes exam takers confuse curtail with curative or curtain because of similar spelling and may wrongly associate it with healing or covering. Others might misread the question and look for an antonym instead of a synonym. Always read the instruction carefully: here it clearly asks for the meaning of the given word. When you see curtail, think of words like reduce, cut down, trim, restrict or downsize. If the option points towards increasing or lengthening, it is likely to be wrong.

Final Answer:
The option that best expresses the meaning of curtail is Downsize.