Which elements do hydrogen fuel cells combine to produce electricity? A. hydrogen and oxygen
B. hydrogen and carbon
C. hydrogen, oxygen, and nitrogen
D. hydrogen, carbon, and nitrogen
PLEASE HELP

As the human population grows, what happens to our natural-resource requirements? o they increase o they decrease o they do not change. they go in cycles

Ascientist discovers a new body between the orbit of neptune and the kuiper belt. the object is round and travels in an orbit around neptune with other space objects. the scientist claims that she has found a new dwarf planet. where is the scientist’s error? the object is an asteroid, not a dwarf planet.the object is a moon, not a dwarf planet.the object is not a dwarf planet because it travels with other objects.the object is not a dwarf planet because it is round.

Currents are caused by temperature and density differences