Nuendo converting to MXF automatically!

My audio files in Nuendo are changed to MXF files unattempted and so silence audio clip after normalize or change 48kHz to 44.kHz Sample Rate.

How to resolve this? Thx!!!

Nuendo 11.0.41
Mac OSX 10.14.6


my mistake.
I didn’t notice the need to choose the audio format before in the Setup Project menu.