单选题 The ______ of medical knowledge is being pushed farther onwards as time goes on.
A. potential B. multitude C. frontier D. leap

【正确答案】 C
【答案解析】[解析] (frontier尖端，新领域)。句意为：随着时间的推移，医学知识的新领域正经历着巨大的进展。A．potential潜能；B．multitude大批，大群；D．leap跳跃。