In terms of cognitive theories explaining generalized anxiety disorder, a good deal of research supports:

A) only metacognitive theory.
B) only intolerance of uncertainty theory.
C) neither metacognitive theory nor intolerance of uncertainty theory.
D) both metacognitive theory and intolerance of uncertainty theory.

Both metacognitive theory and intolerance of uncertainty theory have received substantial support in explaining generalized anxiety disorder. Metacognitive theory suggests that individuals with GAD engage in excessive worry because they believe it helps prevent negative outcomes or prepares them for the worst, while intolerance of uncertainty theory posits that individuals with GAD find uncertain situations intolerable and worry excessively as a way to cope with this intolerance.