Error spotting in English grammar: Visitors to the zoo are amused by the monkeys play in the cages. Identify the part of the sentence that contains a grammatical error, or choose the no error option if the sentence is correct.

Introduction / Context:
This question is another example of error spotting in English grammar. You are given a sentence about visitors at a zoo and how they react to monkeys in cages. The sentence is divided into three labelled parts, with a fourth option indicating that there is no error. Your task is to identify which part contains a grammatical mistake. This type of question is common in competitive exams because it checks your knowledge of verb forms, noun forms, and basic sentence structure in real life contexts.

Given Data / Assumptions:

• The sentence is: Visitors to the zoo are amused by the monkeys play in the cages.
• Part A is Visitors to the zoo.
• Part B is are amused by the monkeys.
• Part C is play in the cages.
• Part D is the no error option.
• We assume that the sentence intends to convey that visitors enjoy watching monkeys performing actions inside cages.

Concept / Approach:
The critical concept here involves the difference between a noun and a verb in the form play and playing. When we say someone is amused by something, the word that follows by can be either a noun phrase or a verb phrase in the ing form functioning as a gerund, such as by the monkeys playing. The original sentence uses play as a bare verb without a helping verb, which disrupts the structure. We must determine where this incorrect usage is located among the labelled parts A, B, and C, and then suggest the correct form that would complete the meaning properly.

Step-by-Step Solution:
Step 1: Examine part A, Visitors to the zoo. This is a correct noun phrase referring to people who go to the zoo. There is no grammatical error here. Step 2: Examine part B, are amused by the monkeys. This is structurally correct. The verb are amused is a passive form, and the phrase by the monkeys introduces the agent or the source of amusement. Step 3: Examine part C, play in the cages. After the preposition by, we normally expect a noun phrase or a phrase like playing in the cages that functions as a noun. The bare verb play without any auxiliary is not correct in this position. Step 4: The intended meaning is that visitors are amused by the monkeys playing in the cages. Therefore, the correct form should be playing, not play. Step 5: Because the error occurs in the final part of the sentence where the verb form is wrong, the incorrect segment is C. Step 6: The corrected sentence would read, Visitors to the zoo are amused by the monkeys playing in the cages.

Verification / Alternative Check:
To verify, consider how similar sentences are constructed in standard English. For example, we say, Children are entertained by clowns performing tricks, not by clowns perform tricks. In each case, the ing form performing or playing is used after the preposition by to function as a gerund phrase. If we keep the verb in its base form play without an auxiliary, the structure becomes ungrammatical. Reading the corrected sentence aloud, Visitors to the zoo are amused by the monkeys playing in the cages, sounds natural and clear, which confirms that changing play to playing is necessary and that the error lies in part C.

Why Other Options Are Wrong:
Option a, part A, Visitors to the zoo, is correct and simply identifies who is being amused, so there is no error there.
Option b, part B, are amused by the monkeys, correctly uses the passive form of the verb and the preposition by to introduce the source of amusement.
Option d, the no error option, is incorrect because the sentence as originally written contains a clear verb form error in part C, so we cannot say there is no error.

Common Pitfalls:
A common mistake is to read the sentence quickly and treat play as suitable because the basic idea is understandable. Some learners also confuse the gerund playing with the simple present play, not realising that after a preposition, the ing form is required. Additionally, students sometimes focus only on subject verb agreement at the beginning of the sentence and ignore errors in later parts. To avoid these pitfalls, it is important to check all segments carefully and remember that prepositions like by, in, and on are usually followed by gerunds or noun phrases, not base verb forms.

Final Answer:
The grammatical error is in part C, where play should be playing. Therefore, the correct answer is C.