Explanation

 The cat's toys are in the corner is the correct use of the apostrophe in possessives

possessive noun is singular, add the apostrophe -s. e.g., cat’s toys

the possessive noun is plural and ends with an -s, just add an apostrophe. e.g., cats’ toys

.Note: 

In JUMS key option C is correct  "The cats' toys are in the corner" 

 But According to our view options B & C both are correct