Observations is the correct answer.
To calculate the atomic mass of a single atom of an element, add up the mass of protons and neutrons. Example: Find the atomic mass of an isotope of carbon that has 7 neutrons
When Oxygen is not available, the cell is forced to produce energy (=ATP) through ANAEROBIC processes, that produce much less energy (about 15 times less), than AEROBIC processes. ... The electron transport chain (ETC) allows the cell to produce energy (ATP) by creating a proton gradient across the mitochondrial membrane. So B.
Im sorry this is late but i just got this answer and i got d projective tests