Final answer:
The oral route is the most appropriate and convenient liquid drug form for home administration of an antimicrobial to treat a systemic infection.
Step-by-step explanation:
Among the liquid drug forms typically administered to treat a systemic infection, oral and parenteral routes are commonly utilized. Oral administration is often preferred for its convenience, especially for home administration. Parenteral refers to routes apart from the digestive tract, encompassing intravenous (IV), intramuscular (IM), and subcutaneous (SC) among others, and may be used when drugs are poorly absorbed from the gastrointestinal tract or when high plasma levels are needed quickly. However, IV administration typically requires professional healthcare settings. Considering convenience for home administration and effectiveness in treating systemic infections, the oral route (A) is the most appropriate and convenient method among the options listed.