The ability to generalize a study's results to different circumstances is known as external validity that suffers from 7 types of threats.
<h3>What are the threats to External Validity?</h3>
There are 7 major threats to external validity.
- The first threat is sampling  bias, in which a sample is not representative of the population. 
- The second threat is history, where an unrelated incident can affect the results. 
- The third threat is observer bias, in which the traits or actions of the experimenter unintentionally affect the results, resulting in bias and other demand features. 
- The fourth threat  is the Hawthorne effect, which describes the propensity for individuals to alter their behaviour merely because they are aware that they are being observed.
- The fifth threat is the Testing Effect, in which the results are impacted by whether a test is administered before or after another. 
- The sixth threat is the aptitude-treatment, which involves the interaction of individual and group factors to affect the dependent variable. 
- The environment, time of day, location, researcher traits, and other variables that restrict the generalizability of the results are included in the seventh threat.
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The true statement about white-tailed deer is that they no longer live in an area they were once found; option D.
<h3>What is true of the White-tailed deer of the Puget sound?</h3>
The passage describes two types of Deer found in the area called Puget Sound.
The passage indicates that the white-tailed deer together with the black-tailed deer were the once the two prevalent deer of the Puget Sound.
However, only the black-tailed deer are more common now as the white-tailed deer has been restricted to the low marshy areas and Islands of the Columbia river.
Although the reason for this decline was not given, but it can be inferred that environmental changes led to the decline of the white-tailed deer in the area of Puget sound.
When species of organisms are not able to fully adapt to changes in their environment, the population of that species of organism will reduce until they eventually are no more found in that environment.
In conclusion, white-tailed deer are no longer common in the Puget Sound.
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The closing agent or an escrow officer