Which of the following statements is true about hydrogen and salt? * a .Both hydrogen and salt are elements.
b, Both hydrogen and salt are compounds.
c Hydrogen is an element and salt is a compound.
d. Hydrogen is a compound and salt is an element.

In the image, layer a is the topmost layer. layer c contains fossils from the precambrian era. layer b contains dinosaur fossils, and layer a contains fossils of mammals. which two statements are supported by this evidence? 1. mammals lived before the precambrian era. 2. dinosaurs and mammals existed in the precambrian era. 3. dinosaurs evolved after precambrian organisms. 4. precambrian organisms evolved after dinosaurs. 5. precambrian organisms were the first life-forms to become fossilized, according to this sample.