The correct answer is A) the lack of high-pressure fuel lines. The main advantage of unit injectors over other fuel injection systems is that they do not require high-pressure fuel lines. Unit injectors integrate the fuel pump, injector, and control mechanism into a single unit, eliminating the need for a centralized high-pressure fuel delivery system. This design reduces the complexity of the fuel system and the potential for fuel leaks, which is a significant advantage over other injection systems that rely on high-pressure fuel lines. The other answer choices are incorrect because they do not represent the primary advantage of unit injectors. While the relatively low injection pressures (B), reduced wear of spray orifices (C), and lessened chance of fuel leaks into the engine sump (D) may be secondary benefits, they are not the main advantage of unit injectors compared to other fuel injection systems.