Answer:
With the bolded word being complexities, the definition is...
parts of something that are hard to understand
Step-by-step explanation:
In order to define the bolded word in this context we need to understand that “the detective novel was hard to follow because of the complexities in the plot.” therefore the right answer should be...
"parts of something that are hard to understand" rather than “the way in which pieces are put together or arranged.”