Step 1: Define human trafficking.
Human trafficking is the illegal recruitment, transportation, and exploitation of persons for forced labor, sexual exploitation, or organ trade.
Step 2: Causes.
Organ extraction, prostitution, and forced marriages are common manifestations of trafficking, driven by poverty, social inequality, and criminal networks.
Step 3: Conclude.
\[
\boxed{\text{All of these (Option D) are causes of human trafficking.}}
\]