Which Statement BEST Reflects Current Research About the Biological Causes

Which statement BEST reflects current research about the biological causes of autism spectrum disorder?

A) So far, researchers have found no biological causes for autism spectrum disorder.
B) The problem is much more likely to be with the brain's anatomy rather than with brain functioning.
C) There are probably multiple biological causes.
D) Neurotransmitter dysfunction explains problems in the cerebellum, but not the brain stem.