A:SARS病毒、颤藻、念珠藻
B:乳酸菌、蓝细菌、大肠杆菌
C:鱼的红细胞、植物叶肉细胞
D:人的皮肤上皮细胞、噬菌体
________a teacher has given permission is a student allowed to enter the classroom.