Which of the following variable declarations is going to result in an error?

variable "example" {

type = object({})

}

variable "example" {}

variable "example" {

description = "This is a test"

type = map

default = {"one" = 1, "two" = 2, "Three" = "3"}

}

variable "example" {

description = "This is a variable description"

type = list(string)

default = {}

}