Because the temperatures vary on high global temperatures and its economy.
Answer:
C. Fe2O3 + 2Al → 2Fe + Al2O3
Answer:
cells are so small because it is structural functional unit of an organism which can be only seen through microscope
I think that the best phrase to fit into the blank is a "scientific theory".
A scientific theory is developed through experiments which use the scientific method, and a theory can be improved if additional data is available or if people provide suggestions which make the theory fit the data better.