Why is the ice cream floating on the root beer

Because the ice cream is less dense than the drink and that allows it to float on top of it.

How are we suppose to know this

There really doesn't seem to be anything remotely advanced about this question, especially for high school.that being said, the actual correct answer may depend on the lesson you received.but i'll use common knowledge to you out here.  an atlas is a map, a flat map which depicts the world, all the continents and large bodies of water and etc.  an almanac is basically a yearly calendar. this depicts all the stuff that happened during the year it was released after, such as important events, sporting stuff, astronomical data, etc. it really depends on what type of almanac you go for.encyclopedias contain vast knowledge about just about everything important around the globe. each encyclopedia is generally focused on a topic and it's relating topics, ordered by each book alphabetically.  information resource can be anything. internet, newspaper, talking dog of pure wisdom (joking), the bible (or the religious book for whatever religion is in question), etc. all of these are considered information resources, as they all provide information on their respective topics (the internet is pretty much all topics)now, once again, your true answer will be based on whatever it is you learned, which i would not know. my answer will simply be using common knowledge.but your answers that line up with weather, sports, and business would be an almanac, information resources, and encyclopedia.  unfortunately, in today's world, they have books for everything. they have almanacs for weather, sports, and business, and they also have encyclopedia's for those as well. and of course, you can find all of that using information resources as well.  the only truly incorrect answer here is atlases.  ~hope this !