Correct statement

This question assesses the correct way to refer to a group of people using an adjective.

• We should help the poor. is the correct statement. In English, when the definite article “the” is placed before an adjective (like “poor,” “rich,” “elderly”), it forms a collective noun phrase referring to the entire group of people possessing that quality. This collective noun is plural and does not take an 's'.
• We should help the poors. is incorrect because adjectives used as collective nouns with “the” do not take a plural 's'.
• We should help a poor. is incorrect. “A poor” refers to one unspecified poor person, which doesn't convey the general sentiment of helping the entire group. To refer to one person, it would be “a poor person.”
• We should help the poor fellows. is grammatically correct but less general and concise than “the poor.” “The poor” is the standard and most idiomatic way to refer to the group.