How can scientists determine what kind of atoms are in stars and nebulas?

When analyzing tree rings, what do scientists assume a thin ring indicates?

According to the cell theory, which describes cells? a. all organisms are composed of multiple cells. b. all cells have the same structure and function. c. cells are found in everything on earth. d. living organisms are not created spontaneously

During photosynthesis, hydrogen ions are most directly used to in the chloroplast pictured above. a) make glucose b) make chlorophyll c) produce carbon dioxide d) drive the production of atp