A) chromosome
b) dna nucleotide
c) codon
d) gene
place the components in order, from smallest to largest.
a) a0b0d0c
b) b0c0d0a
c) c0d0b0a
d) d0c0b0a

Since gene has multiple codons 
and codon has 3 sequence of nucleotides, 

The smallest would be a DNA nucleotide , then a codon, then a gene and finally a chromosome!

so the answer is B

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