Answer: Wendy did not use random assignment
Explanation: Wendy's failure to randomly assign participants or subject to his research will pose a threat to the internal validity of his study. The internal validity of a study simply refers to the structure of an experiment and it's trustworthiness in establishing causal relationship between the applied treatment used a study and the observed outcome. Wendy's decision to ignore random assignment and opt for a manual assignment of subject to each treatment will pose a threat to the structure of his study and hence the establishment of a causal relationship between the treatment t and outcome of the study.
Answer:
the central nervous system and peripheral nervous system
Explanation:
The central nervous system is made up of the brain and spinal cord.
The peripheral nervous system is made up of nerves that branch off from the spinal cord and extend to all parts of the body.