Biological causes of an anxiety disorder include, but are not limited to,
a) genetic influences and chemical imbalances in the brain
b) anxiety sensitivity and pairing neutral stimuli to frightening stimuli
c) our evolutionary history of historically frightening stimuli
d) our capacity of observing, retaining, and replicating behavior

A) genetic influences and chemical imbalances in the brain

Explanation:

An anxiety disorder is a psychiatric disorder where the individual experiences an excessive and irrational worry in everyday situations. Generalized anxiety disorder, phobias, panic attacks, etc are examples of anxiety disorders.

Anxiety does not have a specific cause, it can be the result of different factors like changes in the brain's chemistry, environmental stress or even genetics.

I hope you find this information useful and interesting! Good luck!

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."

did you fail the test? xd