a question about a part of a reading

[Morvarid798]

Autism is a developmental disorder that is characterized by severe behavioral abnormalities across all primary areas of functioning.

Q:The word primary in the passage could best be replaced by
a)elementary
b)main
c)introductory
d)primitive

How can I know that main is the best answer.please describe for me.

[Beeesneees]

Have you tried looking up the definition of 'primary' in a dictionary?

Look at definition number 1 here and you will underastand why 'main' is the best alternative:
http://www.oxfordadvancedlearnersdictionary.com/dictionary/primary
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Cheers m' dears!

[Morvarid798]

I know that one of the meaning of primary is main,but i wasn't sure about this sentence because I don't understand the second part of sentence "across all primary areas of functioning".

[Beeesneees]

It is talking about the function of the brain and body.
_________________
Cheers m' dears!