Final answer:
The sentence indicating research into the debate on cellphones in schools is option B, which acknowledges the discussion around the necessity and place of cellphones in educational settings.
Step-by-step explanation:
The sentence from the text that best supports the inference that the author researched the issue of allowing cellphones in school is: B) Despite students' needs to use cell phones in schools, it has become a debate on whether or not they belong in schools.
This sentence suggests a level of engagement with the debate and implies that there has been research into the various views on this issue. It captures the essence of the controversy by acknowledging the debate itself, implying that different arguments and perspectives have been considered.
The mention of a school principal in option C) also suggests research, but it is a direct statement that does not clearly indicate an investigation into the broader issue.