Need help on shortlisting field of work

hello,

I am shortlisting the field within Mechanical engineering for which I want to apply for a Masters Degree but am facing difficulty in narrowing it down to a field.
As part of my Bachelors i have worked on CFD related projects.(Involved C and Matlab coding)
I have also done a project related to vibrations.
In my current job I am working on Aircraft Simulators.
I have shortlisted the following fields:
Applied Mechanics
Automotive & Aircraft Engines
Computational Fluid Dynamics
Fluid Mechanics
Heat and Mass Transfer
Internal and External Combustion Engines
Systems Design and Management
Thermodynamics

Any help in this regard would be helpful?
Is switching off fields possible while doing the degree?

Thanks