The most appropriate completion of the sentence based on the provided options is:

All of the above.

This is because each statement addresses a different aspect of the theodicy problem, which is the question of why a good and powerful God would allow suffering:

1. Humanity, through the fall, is primarily responsible for suffering.
   • This refers to the doctrine of original sin and the fall of man, which suggests that suffering entered the world through human actions.
2. God could only avoid suffering for humanity by removing free will, but this would avoid love as well.
   • This addresses the argument that free will is necessary for genuine love and moral choices, and that the possibility of suffering is a consequence of free will.
3. Suffering seems to represent a great injustice, but God will fulfill all justice at the right time.
   • This statement reflects the belief in ultimate divine justice, where all wrongs will be righted and all suffering will be accounted for in the fullness of time.