سوال ۱ کنکور ارشد مهندسی برق ۱۴۰۵

The fixed collocation is "a source of information" — a source is the origin or provider from which information comes. The sentence warns that Instagram is not a reliable place to get medical information, i.e. not a good source. "discovery" (something found for the first time), "cause" (what makes something happen), and "agreement" (a mutual arrangement) do not combine with "of ... information" and do not fit the meaning.