The Bubonic plague and the raids by Vikings.
Answer:
A
Explanation:
These archers could demolish the other from afar, creating mangaldai.
Have a godly day!
A two way treaty.. two parties come together
Answer: Selection bias
Explanation:
Selection bias is defined as the process in which individual or group of individual are analyzed for selection process by lacking randomization property .This process displays that selected sample of individuals is not similar representative of major interest population.
According to the question,the systematic difference that occurs in selected group for experiment as per their last name is displaying that selected group does not represent interest population that is causing systematic error.Thus, this situation describes about selection biasing.