Although the actual questions are missing from your ask, here's how you can tell.
If the study will be messed up (added bias) through interaction with the subjects the study should be observational. For example if a biologists wanted to study the eating habits of wild birds in the tropics, they would need to do an observational study. if they did a controlled experiment, the birds will change their eating habits based on human interaction, thus making the study invalid.
If the study requires specific measurements, close monitoring, or contact and interaction with the subjects the study should be a controlled experiment. For example, if a scientist wanted to test out a new drug, the health of patients would need to be closely monitored.
Answer:
pigs
Explanation:
Influenza is an infectious disease caused by influenza viruses, which can be divided into four types A, B, C and D. In humans, influenza A and B viruses are known to cause epidemics, while A viruses are known to cause pandemics. Influenza viruses are also found in birds and mammals (e.g., dogs, cats, cattle pigs and horses). Cross-species virus transmission refers to the transmission process of infectious viruses between hosts from different species. Several viruses that may cause severe diseases in humans have originated from animal species, e.g., avian influenza A virus that can be transmitted to humans through an intermediate host (e.g., pigs). Other examples of cross-species virus transmission include the Ebola virus and Hantaviruses. It has been suggested that cross-species transmission is a common phenomenon in rapidly evolving viruses.
Answer:
me and u
Explanation:
a and b me but and you like me
Answer:
the branch of science concerned with classification, especially of organisms; systematics.
Explanation: