Answer:
The sentence that correctly uses apostrophes to show joint ownership is the following one: Marina and Kayla's toys are under the bed.
Explanation:
The sentence above contains a compound subject. That is, two simple subjects have been joined by a coordinating conjunction and share the same predicate. In this case, the subjects own the same toys. If both nouns part of a compound subject own the same thing, the apostrophe is placed after the last noun (Kayla's).
