下列有关YAC描述，错误的是() ["A．为线状DNA分子","B．由着丝粒、端粒、复制子和外源DNA构成","C．培养方便","D．可表达真核细胞基因","E．装载容量少是它的缺点"] 原发性肝癌与下列哪些因素无关() ["A．抑癌基因p53突变","B．HBV感染","C．HDV感染","D．黄曲霉素摄入","E．染色体突变"] 患者，男性，42岁，数月来右下后牙常进食后疼痛，偶自发痛及冷、热刺激痛，自服抗生素可缓解，1天前进食后复发。检查：见口腔卫生差，龈上、下结石多，牙龈轻度充血水肿，右下678牙体完整，右下7叩(+)，右下8颊向错位，伸长无对颌，右下8与右下7之间有较多食物残渣，龈乳头中度充血水肿，压痛，未探及牙周袋，右下678X线片未见异常。导致该症状出现的促进因素是() ["A．牙石","B．食物嵌塞","C．创伤","D．错畸形","E．牙菌斑"] 引物Tm值的计算公式为() ["A．4(A+T)+2(C+G)","B．4(A+T)+4(C+G)","C．2(A+T)+4(C+G)","D．2(A+T)+2(C+G)","E．3(A+T)+3(C+G)"] 患者，男性，26岁，体健。主诉：牙龈自动出血伴牙龈疼痛，腐败性口臭5天。此患者最佳首诊治疗措施是() ["A．去除大块牙石及坏死物，3%双氧水冲洗","B．彻底去除大块牙石及坏死物，3%双氧水冲洗","C．保守治疗，需查血确诊","D．口服抗生素及维生素C","E．1%～2%双氧水含漱1周"] PIR和PSD数据库是()