I chose D.. Writing the POE for this one seems tough, but I will try..
POE,
A. It is remarkable anyone ever sleeps... based on the complexity... ? That does not make sense. We need to show cause and effect. "based on" is incorrectly used.
B. With (preposition)+ noun + present participle - construction is used.. this construction is acceptable when we genuinely refer to a noun.. here the entire action of orchestrating can be appropriately expressed as a subordinate clause.
Also, 2 other point here..
various human body systems? that sounds awkward - it should be various systems of the human body
VAN - Verb>Adjective>Noun is preferred in GMAT. So let us look at other options
C. Here .. the human body involved in sleeping appears incorrect. it should be the systems that are involved in sleeping
D. Everything looks fine.
Given the complexity - cause and effect is established
Adjective orchestrating > noun orchestration
various
systems of the human body that are involved in sleeping - correctly used
E. Not sure what the pronoun it refers to.. human body systems - sounds awkward