Q: 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
B. allow it to draw in its exposed parts, and so
C. allows for it to draw in its exposed parts and that
D. allows that it can draw in its exposed parts, and so
E. allows it to draw in its exposed parts, so that

OA D

I eliminated A,B,C answer choices. How is D the correct answer here? Why not E? Isn't allows it more idiomatic than allows that it?

Please let me know.
Thanks.