The Cretaceous-Tertiary extinction event , the name given to the die off dinosaurs, they all died off about 65.5 million years ago . They died by climate and geological changes .
Im sorry but its a pdf i can write on it :(
It's simply, e.g. I'm from Poland, imagine that you give me strong acid (HF, dangerous corrosive substance), so how can I recognize that this substance is dangerous? Safety symbols on all hazardous products are <span>requirement in chemistry.</span>