Answer:
Electrical Engineering, and, more specifically, Power Systems Engineering (or simply, Power Engineering).
Explanation:
The words high voltage and lines refer to power transmission lines (transmission of electricity). <em>Power transmissions lines</em> are the main concern of the <em>electric power transmission</em>, which is, at the same time, part of the subfield of the <em>Electrical Engineering</em> called <em>Power Systems Engineering </em>or simply <em>Power Engineering</em>, which "deals with the generation, <em>transmission</em>, <em>distribution</em> and utilization of electric power, and the electrical apparatus connected to such systems" <em>Power Engineering</em> (2020), in <em>Wikipedia</em>.
Then, the career that best fits this group of words is, therefore, <em>Electrical Engineering, and, more specifically, as a subfield of it, </em>the Power Systems Engineering.