Why I cannot root my ZTE Z981 Tmobile Phone

[Android Central Question]

Hi, I am having a lot of trouble rooting my ZTE Z981 Tmobile Phone. I have tried at least 5 apps to do the rooting they all keep failing. I have enabled debugging and also disabled other suggested programs that can hinder the root process. Can someone please suggest what could be wrong. Thank

 

[belodion]

A locked bootloader?