A Relation is said to be a Function if an element of Domain of the Function has one and only one image in the Co-domain of the Function.
⇒ A is not a Function, Because Element 4 has Three images
⇒ B is a Function, Because Each Element has a Unique Image
⇒ C is not a Function, Because Element 7 has Two images
⇒ D is a Function, Because Each Element has a Unique Image
⇒ E is a Function, Because Each Element has a Unique Image
So, The Relations which are Functions are : B - D - E