The particular design of muscles and bones in the neck and limbs of the turtle
allow that it can draw in its exposed parts such that an attacker can find nothing but hard shell to bite.
A. allow that it can draw in its exposed parts such that - subject-verb agreement issue - design needs allows
B. allow it to draw in its exposed parts, and so - subject-verb agreement issue - design needs allows
C. allows for it to draw in its exposed parts and that - usage of and changes the meaning
D. allows that it can draw in its exposed parts, and so - "Allow that (noun) (verb)" is not idiomatic. "Allow (noun) to (verb)" is the correct form.
* "And so" should introduce a consequence of whatever is described by the entire sentence preceding it.
For instance,
The turtle retracted all of its exposed parts into its shell, and so its attackers were unable to find anything to bite.
--> This sentence is fine, because the part after "and so" is a consequence of everything described in the main sentence ("The turtle retracted...")
In the sentence here, the second part is not a consequence of the entire main part of the sentence.
E. allows it to draw in its exposed parts, so that - Correct
Answer E
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