The correct answer is: E. No error
The sentence is grammatically correct. The subject and verb agree, and the sentence is complete. The prepositional phrase “of the recognition of this fact” modifies the verb “are seen.” The prepositional phrase “in the gradual improvement of the diet of the poor” modifies the noun “results.”
The sentence could be improved by adding more detail. For example, the writer could explain what the recognition of this fact is, or what the gradual improvement of the diet of the poor means. The writer could also provide more evidence to support the claim that the results of the recognition of this fact are seen in the gradual improvement of the diet of the poor.