System administrator - what specialty to choose?

Question

IT education

Hello. I decided to retrain from "enikeev" to administrators, namely to get a secondary specialized education. There are three specialties at once, which seem to give an entry in the diploma "computer technician" (simplified):
1) Computer networks
2) Computer systems and complexes
3) Information security of automated
systems studies in any of the above areas, you can go to work at least as an assistant to the administrator. So the question is, are these specialties very different? Are there people here who graduated from one of the above? What is better to choose the future system. admin?