Need help figuring out the answer to this question. I guessed C but I don't know if it's correct and I don't know how to figure out the correct answer.

10. How many different constitutional isomers are formed upon radical monochlorination of 4methylheptane? (Since this question asks for constitutional isomers, do not consider stereoisomers.) \begin{tabular}{cccc|c} A & B & C & D \\ 1 & 5 & 6 & 8 & \end{tabular}