Final answer:
Ricky Skaggs (option D) is the performer who transitioned from bluegrass to country music and achieved stardom.
Step-by-step explanation:
The performer who crossed over to country from bluegrass and became a big star is Ricky Skaggs (option D) . Known for his mastery of the mandolin, Skaggs was a child prodigy in bluegrass before he transitioned into mainstream country music. Throughout the 1980s, Ricky Skaggs became a significant figure in country music, bringing traditional bluegrass influences to the genre and striking a chord with audiences who appreciated his blend of authenticity and innovation.