The right answer is the alternative "C. Harvey's Pretzel Stand will close due to its inability to secure the special salts needed for the pretzels."
This is the right alternative because an organization of cause and effect refers to the relation of two consecutive events, where one was caused by the other.
The alternative letter C is the only one that expresses this. The phrase "Harvey's Pretzel Stand will close" is the effect. This will close "because of their inability to ensure the special salts needed for the pretzels." which is the cause.