>>1707695[Point taken. I'll stick with [A], if only because all 3 options are likely subject to Murphy's Law (from her POV).]
>>1707751[Like Saki said, it's from the Railgun manga. The beach omake chapter, to be precise.]
http://www.mangahere.co/manga/to_aru_kagaku_no_rail_gun/v07/c044.5/