The word "credible" means something we can believe in, that is, something that is reliable. Thus, when we ask if a given source is credible, we want to know if that source gives true, scientifically confirmed and correct information. For this reason, we can say that if Evander wants to know if an information is reliable, he should ask "Is the source credible?", If the answer is yes, it means that the information is reliable, but if the answer is no or maybe, Evander should not trust and look for correct information elsewhere.
An asthma attack is when the muscles in your airway swell up, causing your airways so shrink. This is due to an allergic reaction, in witch you inhale something and your body "over reacts" to it.