extra fee额外费用extraadj.额外的n.额外之物；临时演员adv.特别地extracurricular reading material课外读物extraordinarily high temperature超高温extracurricular sports exercises中学生extra fine stainless steel wires极细丝extra-cavity resonant doubling外腔谐振倍频extracellular protease secretion胞外酶分泌extrahepatic biliary obstruction肝外胆管梗阻extraembryonic capillary network胚外毛细血管网extra-adrenal pheochromocytoma肾上腺外嗜铬细胞瘤extrachromosomal genetic element染色体外遗传因子