A. This is an observation. There are research data to support the statement.
B. This is an inference. Based on the information presented, the research supports this conclusion.
C. This is the best answer. This is a guiding belief for the subsequent research. Although one might argue that the supporting evidence leads to this conclusion, it is an assumption that deterioration is the explanation for retrieval difficulties.
D. This is an inference. Research investigations are presented to support the probability of relearning the material quickly.
E. This is an observation. The statement is specifically supported by research results.