imo -- A

B, C and D are awkard and wordy.
E -- "Who" cannot refer "individual responses"

Thanks

'that' correctly modifies emotional reactions. There is a cause and effect in the sentence.
Emotional reactions cause physiological responses. Therefore A correctly shows this cause effect relationship.

(A) that, in turn, create unconscious physiological responses [Nothing wrong with this option!Correct!]

(B) that creates unconscious physiological responses in turn [subject verb agreement error. creates- singular. emotional reactions- plural. Eliminated!]

(C) creating, in turn, unconscious physiological responses [creating modifies individual. The individual is not creating physiological responses. Eliminated!]

(D) to create, in turn, physiological responses that are unconscious [OMG!!from when did physiological responses become unconscious? are responses conscious also? Eliminated!]

(E) who creates unconscious physiological responses in turn [SV agreement error. Eliminated!]

Hope this helps!

Fibo,

Seems we need to learn a lot form you for posting simple/neat/explanatory posts!!

I really appreciate the effort u take to post "quality posts"

Cheers UP!!