The correct answer is খ) is.
When a subject is connected with "along with," the verb agrees with the main subject, not the one introduced by "along with." In this case, "the man" is the main subject, and the phrase "along with his neighbours" does not affect the singular form of the verb. Therefore, the correct sentence is:
"The man along with his neighbours is working for the welfare of the people."
Explanation for the incorrect options:
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ক) have: This verb is plural and would be used if the subject was plural, such as "the man and his neighbours." Since the main subject is singular, this option is incorrect.
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গ) were: This verb is in the past tense and would be used if we were talking about something that happened in the past. In this case, the sentence is in the present tense, making this option incorrect.
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ঘ) are: This verb is plural and would be correct if the subject were plural, such as "the man and his neighbours." However, the main subject here is "the man," which is singular. Hence, this option is incorrect.
By following the rule that the verb must agree with the main subject "the man," the correct choice is is.