Avogadro's hypothesis states that:
A. When two elements form a series of compounds, the ratios of masses that combine with 1 gram of the first element can always be reduced to small whole numbers.
B. A given compound always contains exactly the same proportion of elements by mass.
C. Mass is neither created nor destroyed in a chemical reaction.
D. At the same temperature and pressure, equal volumes of different gases contain an equal number of particles.
E. Each atom of oxygen is 16 times more massive than an atom of hydrogen.