Step 1: State the theory.
Richard Lazarus proposed the {cognitive appraisal} model: stress depends on how a person {appraises} an event (primary appraisal: threat/challenge; secondary: coping resources), not just on the event itself.
Step 2: Rule out others.
Spearman and Thurstone are intelligence theorists (g and primary mental abilities), unrelated to stress theory.
\[
\boxed{\text{(A) Lazarus.}}
\]