Please respond to the following questions either by writing

Please respond to the following questions either by writing the design name or by describing the design using standard notation (X = program, O=observation, R= random assignment). For each design, please discuss all threats to internal validity.
1. a. Design: Single group post-test only
b. Internal validity threats:
2. a. Design: (R) O1 X O2
(R) O1 O2
b. Internal validity threats:
3. a. Design: Pretest-posttest design with experimental and comparison group
b. Internal validity threats:
4. a. Design: O X O
b. Internal validity threats:
5. a. Design: Single group with three pretests and four posttests
b. Internal validity threats: