A. 职业差异 B. 职务差异 C. 地区差异 D. 性别差异
A. 正确 B. 错误
A. 无色透明 B. 两侧不对称,一侧扁平,一侧稍凸 C. 卵自虫体排出时,卵内胚胎已发育至蝌蚪期 D. 感染期卵内含一条盘曲的幼虫 E. 卵壳外有凹凸不平的蛋白膜
A. they must be unique in a database B. they can only be used once in a view C. they can only used once on each form D. they can be used mulriple times on a form&e