Grace Is Sitting in Class When,without Warning,her Heart Began to Pound,her

Grace is sitting in class when,without warning,her heart began to pound,her chest felt tight,and a feeling of dizziness came over her.She felt extremely fearful.Over the next few weeks,the same thing happened several times.Her doctor cannot find anything wrong with her heart.Grace is probably suffering from ____.

A) generalized anxiety disorder
B) obsessive-compulsive disorder
C) panic disorder
D) a phobia