Explanation:

- Statement 1: "They go" is grammatically correct. It is in the simple present tense, which is often used to describe habitual actions.

- Statement 2: "to Agra" is a correct prepositional phrase, indicating the destination.

- Statement 3: "during summer vacations" should be "during the summer vacation" to be grammatically correct. Using "the" is appropriate for specific vacations and "vacation" generally refers to a singular period of vacation time.

- Option 1: Incorrect. Statement 1 has no error.

- Option 2: Incorrect. Statement 2 has no error.

- Option 3: Correct. Statement 3 contains an error related to the use of articles and singular/plural form.

- Option 4: Incorrect. There is an error in statement 3, so choosing "No error" is not correct.

Correct Answer: Option 3: 3