What are infectious agents? A. agents that investigate different types of infection
B. attackers that cause a response by the immune system
C. attackers that cannot cause a response by the immune system
D. infectious agents are always good for the human system.

What is a quantitative observation? a. an observation that proves the hypothesis is wrong. b. an observation about the number or amount of something. c. an observation about the color, shape, size, or condition of something. d. an observation in which the appearance of something is described using descriptive language.