The restorer line is represented as

The correct answer is Option A: R-line.
Let's break down why:
In the context of hybrid seed production, especially in crops like rice and maize, we use different lines with specific roles.
A-line (Male-sterile line): This line is unable to produce functional pollen. It's used as the female parent in hybrid seed production.
B-line (Maintainer line): This line is used to maintain the A-line. It's genetically similar to the A-line but possesses normal pollen fertility.
R-line (Restorer line): This line carries a fertility restorer gene (Rf gene). When it pollinates the A-line (which is male-sterile), the resulting hybrid offspring regain fertility. So, the hybrid plant can produce viable seeds.
C-line: While C-lines might be used in some specific breeding programs, it's not a standard term associated with the restorer system. It generally doesn't directly represent the restorer line in hybrid seed production.
Therefore, the restorer line is specifically represented as the R-line because it's responsible for restoring fertility in the hybrid progeny.