Final answer:
The major sources of confound in between-subjects designs are Selection Bias and History, which studies control for using control groups, random assignments, and blinding to ensure accurate experimental results.
Step-by-step explanation:
The two major sources of confounds that exist in between-subjects designs are Selection Bias and History. Selection bias occurs when participants in different groups have different characteristics before the experiment begins, leading to biased outcomes. History refers to external events that occur between the start and end of the experiment which may affect the participants' responses.
Experimental design principles, including the use of control groups, random assignment, the placebo effect, and blinding, as well as taking into account lurking variables, are crucial strategies employed to mitigate these confounds and to isolate the explanatory variable's impact on the response variable.