Final answer:
The conjunction for joining items of unequal rank is 'Because', which is a subordinating conjunction that connects an independent clause with a dependent clause.
Step-by-step explanation:
The conjunction that would join items of unequal rank is 'd. Because'. This is because 'because' is a subordinating conjunction that is used to join an independent clause with a dependent clause, thus creating a complex sentence. Coordinating conjunctions like 'for', 'and', 'but', 'or', 'yet', and 'so', represented by the acronym FANBOYS, are used to connect items of equal grammatical rank, typically two independent clauses. The examples provided in the question reflect coordinating conjunctions, not subordinating ones that would create a hierarchy in the sentence structure.