You use it by first making a observation, second ask questions, third do background research, and fourth form a hypothesis
Answer:
More specifically, transmission occurs when the agent leaves its reservoir or host through a portal of exit, is conveyed by some mode of transmission, and enters through an appropriate portal of entry to infect a susceptible host. This sequence is sometimes called the chain of infection.
1) the answer is D
2) the answer is D
3) the answer is B
