Final answer:
The compound sentence in the passage is "Stingrays can be friendly in a marine environment, and some of them can even be hand fed and petted," as it contains two independent clauses connected by "and."
Step-by-step explanation:
Looking at the provided passage from "The Venomous Ray," we can identify the compound sentence by finding a sentence that has at least two independent clauses usually connected by a coordinating conjunction. In the passage, the sentence "Stingrays can be friendly in a marine environment, and some of them can even be hand fed and petted" is the compound sentence. It contains two independent clauses: "Stingrays can be friendly in a marine environment" and "some of them can even be hand fed and petted," which are joined by the conjunction "and."