Based on the data in figure $1$ and $2,$ how many thumb drives had plugged into the system by the user $($whose $"\backslash$Software$\backslash$Microsoft$\backslash$Windows$\backslash$CurrentVersion$\backslash$Explorer$\backslash$MountPoints$2"$ key's subkeys are shown in Figure $2)?$

a$)0$

b$)3$

c$)6$