Concept:
Seed production follows a fixed sequence to maintain genetic purity and quality.
Step 1: Nucleus seed.
Nucleus seed is the first and purest seed maintained by the breeder.
\[
\text{First step}=C
\]
Step 2: Breeder seed.
Breeder seed is produced from nucleus seed under the supervision of the plant breeder.
\[
\text{Second step}=B
\]
Step 3: Foundation seed.
Foundation seed is produced from breeder seed.
\[
\text{Third step}=D
\]
Step 4: Certified seed.
Certified seed is produced from foundation seed and supplied to farmers for cultivation.
\[
\text{Fourth step}=A
\]
Therefore, the correct sequence is:
\[
C,B,D,A
\]
\[
\therefore \text{Correct Answer is (C)}
\]