This warm air was, needless to say, the perfect environment for the rapid growth of disease-carrying ________originating from outside the building.
句意：毋庸置疑，这样温暖的空气是导致从室外而来的病菌迅速滋生的完美的环境。germ微生物，细菌，病菌。microbe微生物。fungus真菌，霉菌。bacteria（复数）细菌。此处应当用复数。因此，本题的正确答案为D。