In the following sentence, choose the alternative that best improves the underlined phrase related to subject–verb agreement. At the present rate of exchange, fourteen dozen cost Rs 3000.

Introduction / Context:
This question tests knowledge of subject verb agreement in English grammar, especially when numbers are used with units of measurement such as dozen. Competitive exams often check whether candidates can recognise when a plural subject requires a plural verb even when a unit word like dozen appears without a visible plural s. Understanding this pattern is important because it appears frequently in questions about quantities, prices, and commercial expressions.

Given Data / Assumptions:
• The sentence is: At the present rate of exchange, fourteen dozen cost Rs 3000.• The underlined part concerns the verb agreeing with fourteen dozen.• We assume the context is general pricing at a given rate of exchange.

Concept / Approach:
In English, when a number is followed by a unit like dozen, hundred, thousand, litre or kilogram and the idea is a countable quantity, the grammatical subject is considered plural if the number is more than one. Therefore, a plural subject such as fourteen dozen requires a plural verb like cost, not a singular verb like costs. The phrase fourteen dozen is treated as a plural noun phrase because it represents many individual items.

Step-by-Step Solution:
Step 1: Identify the subject of the verb. The full subject is fourteen dozen, which clearly expresses a quantity greater than one.Step 2: Decide whether the subject is grammatically singular or plural. Since fourteen is greater than one, the phrase is plural in meaning and grammar.Step 3: Match the verb with the subject. A plural subject must take a plural verb, so the correct verb form is cost, not costs.Step 4: Check the entire sentence: At the present rate of exchange, fourteen dozen cost Rs 3000. The sentence is grammatically correct as written.Step 5: Therefore, no change is required, and the correct choice is No improvement.

Verification / Alternative check:
You can verify by substituting other numbers. For example, one dozen costs Rs 200, but two dozen cost Rs 400. When the number is one, the subject is singular and you use costs. When the number is more than one, the subject is plural and you use cost. The original sentence follows this same pattern with fourteen dozen, so the existing form is correct.

Why Other Options Are Wrong:
Option a: dozen costs is incorrect because dozen without a number usually implies a singular unit, but the sentence clearly refers to fourteen dozen, not one dozen.Option b: dozens cost is awkward and unidiomatic here. We normally keep dozen in the singular form after a numeral, such as fourteen dozen, not fourteen dozens.Option c: dozens costs is wrong for two reasons. Dozens is plural, so it should not pair with the singular verb costs, and the phrase fourteen dozens is not standard usage.

Common Pitfalls:
A common mistake is to look only at the nearest noun and forget the number before it. Some learners think that because dozen does not have an s in the phrase fourteen dozen, it must be singular. In reality, the number determines the grammatical number of the phrase. It is also easy to confuse commercial expressions like a dozen eggs, three pair of shoes and twenty head of cattle, where the unit nouns stay singular even though the entire phrase is plural. Remember that the verb must agree with the overall quantity, not with the visible s at the end of the unit word.

Final Answer:
The sentence already uses the correct plural verb with the plural subject fourteen dozen, so no change is required. Correct answer: No improvement.