I can't save if this will work on a C67ML, but on an M96 Plus and T68 Plus I used King Root (the pc version, not the android version). That rooted the devices, and I subsequently used Supersu-me PRO to switch the root to SuperSu. I emphasize the pro because if you use the free Supersu-Me it only temporarily switches you from King Root to SuperSu and you lose all root upon rebooting. Pro makes it permanent.
As I said, however, I only have a T68 and M96, not a C67ML.
Here's a thread on rooting a C67ML that google turned up:
https://www.mobileread.com/forums/sho...d.php?t=254238