* Subject-Verb Agreement: The subject is "researcher," which is singular. The verb "explain" needs to be singular as well, so it should be "explains."
* Missing Article: The phrase "such claimed to be use" is unclear. It needs an article before "claimed," like "such *a* claimed to be use."
* Confusing Prepositional Phrase: The phrase "with all his assistants" modifies the researcher, but it doesn't quite make sense in the current context.
* Missing Object: The sentence lacks a direct object for the verb "explains." What is the researcher explaining?
Here's how you could rewrite the sentence to make it grammatically correct and clear:
* "The researcher, with the help of his assistants, explains why this claim is said to be useful."
This version:
* Uses the correct subject-verb agreement.
* Includes an article and clarifies the meaning of "such claimed to be use."
* Provides a direct object for the verb "explains."
Let me know if you'd like to explore other ways to rewrite the sentence!