Step 1: Understand codon definition.
A codon is a sequence of three nucleotide bases in mRNA.
So:
\[
A = 3 \text{ bases}
\]
Step 2: What does codon specify?
Each codon codes for a specific amino acid.
So:
\[
B = \text{amino acid}
\]
Step 3: Where is amino acid incorporated?
Amino acids are incorporated into polypeptide chain which forms protein.
So:
\[
C = \text{protein}
\]
Final Answer:
\[
\boxed{3\text{ bases, amino acid, protein}}
\]