Answer:
a. truth bias
Step-by-step explanation:
Truth bias: Th term truth bias is defined as the phenomenon through which a person assumes that his or her partner is telling the truth even in the absence of any particular evidence. It occurs because mostly partners tell the truth.
In other words, people tend to believe others without having a shred of evidence to the contrary, and often considered as normal because people do trust each other completely who shares a good bond.
In the question above, Cassie’s inability to suspect Nathan of cheating demonstrates the concept of truth bias.