It's possible that you could get the information you need from ANY of them. But it's true that if you need the info in a hurry, and it absolutely positively has to be correct, then you should approach them in kind of the order of what the probability is that you'll get the straight, correct story.
To me, here's how I would line them up in the order of probability:
Tops: a scientist specializing in that particular field next a scientist specializing in a different field next a university professor who teaches that particular field next a university professor who teaches a different field next a librarian, who may not know it but definitely knows where to find it next my parents next my teacher last my friends (nothing against my friends, but if it has to be fast and accurate, then I may not have the time to wait for my friend to find it, or the time to check it out after I get it from my friend)
When a lightning bolt travels from the cloud to the ground it actually opens up a little hole in the air, called a channel. Once then light is gone the air collapses back in and creates a sound wave that we hear as thunder. The reason we see lightning before we hear thunder is because light travels faster than sound!
