crij assignemnt

please answer all questions listed below. Answers should be written in full paragraphs, utilize standard 12 pt. font, have 1 inch margins, and be free of grammatical and spelling errors. There is no length requirement for your assignment, but you must answer all questions completely. Your assignment should be submitted via the link below.
Identify and discuss two threats to internal validity in experimental designs. Include in your answer ways of controlling for each of the threats you identify.
Select two probability sampling techniques and explain why each is an example of probability. Give an example of a research project that would be appropriate for each sampling technique.
Select two non-probability sampling techniques and explain why each is an example of non-probability. Give an example of a research project that would be appropriate for each sampling technique.