The use of lie detectors is based on the assumption that lying produce

The use of lie detectors is based on the assumption that lying produces emotional reactions in an individual that, in turn, create unconscious physiological responses.

(A) that, in turn, create unconscious physiological responses
(B) that creates unconscious physiological responses in turn
(C) creating, in turn, unconscious physiological responses
(D) to create, in turn, physiological responses that are unconscious
(E) who creates unconscious physiological responses in turn

The easiest place to start is probably with the create/creates split. What "create(s)...responses"? The emotional reaction. (Strictly speaking the subject of the verb "create" is the pronoun "that." More on this issue later.) Since "emotional reactions" is plural, we want a plural verb, "create." That eliminates B and E. "Creating" in C is a present participle, and "to create" in D is an infinitive, so neither of these is either singular or plural.

Next we might consider which form of the verb "create" is appropriate, the verb "create," the present participle "creating," or the infinitive "to create." A verb-form split usually signals either an idiom problem or a problem with parallelism, but not in this case. Rather, neither C nor D captures the original meaning. Answer C: A present participle (-ing word) immediately preceded by a noun (no comma separating them) attributes action to that noun. So C means that "an individual" creates responses. Answer D: Here, "to create" suggests that the goal of producing emotional reactions is to create physiological responses.

That leaves A, the correct answer.

Addendum 1. I began by asking "What creates responses?" This common-sense question is usually adequate to match a verb to its subject. Sometimes you'll have a couple of reasonable answers, and you'll have to look more closely at the grammar. The verbs in relative clauses--noun-modifying clauses that start with "that" or one of the "wh-" words, "which," "who/m," "when," "where"--actually modify the relative pronouns that precede them, but those relative pronouns are themselves singular or plural depending on the nouns to which they refer. The long and short of it is that you're probably better off with the common-sense question than with the subtle grammatical question here.

Addendum 2. With few exceptions, relative clauses modify the nouns or noun phrases they touch. In this question, "that...create...responses" touches the noun "individual," but it also touches the noun phrase "emotional reactions in an individual," that is, the noun "reactions" plus the adjective "emotional" plus the prepositional phrase "in an individual." That whole phrase, or if you prefer the noun at its heart, is modified by the relative clause. Frankly, I think that it's a little clumsy here, and I might have had a bit of trouble had I started with the modifier issue.