Final answer:
To concatenate three character vectors into a character vector called fullname, you combine firstname, a space, and lastname with a plus sign (+) in between each in a programming language like Python.
Step-by-step explanation:
To create a character vector fullname by concatenating three character vectors: firstname, a space, and lastname, you can use the following statement in a programming language such as Python:
fullname = firstname + ' ' + lastname
Replace firstname and lastname with the appropriate variable names holding your first and last name respectively. In some programming languages, you might need to use different syntax or functions to concatenate strings.