Which of the following correctly completes the sentence: "There is a girl ___ has talent."?

The most appropriate word to complete the sentence "There is a girl ___ has talent." is "who." This is because "who" is a relative pronoun used to refer to people. It connects the noun "girl" to the additional information that "has talent," indicating a characteristic of the girl being discussed.

In this context, "who" indicates that the girl possesses talent and serves to emphasize her identity. This use aligns with standard English grammar conventions for referring to human subjects.

Other options do not fit this usage: "whom" is typically used as an object of a verb or preposition and would not be correct in this subject position. "Which" is used for animals or things, while "that" can refer to people but is less formal and is generally used in restrictive clauses, which are not necessary in this sentence structure. Therefore, "who" is the clearest and most grammatically correct choice to convey the intended meaning about the girl.