Which one of the statements below is true? A. When two atoms combine, they do so in definite proportions by mass?
B. When two different compounds combine to form a compound, they do so in definite proportions by mass.
C. When two different elements combine to form a compound, they do so in definite proportions by mass
D. When two molecules combine, they do so in definite proportions by mass
E. When two different elements combine to form a mixture, they do so in definite proportions by mass