Could you please explain why E is wrong? I did not choose C because “their grandparents would have found miraculous” is missing an object (what do the grandparents find miraculous?)
This is a simple rule we mentioned in the class - in non-restrictive attributive clause we use “which” whereas in restrictive attributive clause we only use “that” to refer to something.
Also, it does not miss an object, the object is appliances. As it serves as object in the attributive clause and therefore it is omitted.