What Are LoxP Sites, and for Which Purpose Are They

What are loxP sites, and for which purpose are they used?

A) Cleavage sites for a class of restriction endonucleases that are popular for recombinant DNA studies.
B) Recombination sites that are recognized by a Cre recombinase, used for the targeted excision of genes.
C) Integration sites for retroviral vectors that are used for targeted gene insertion.
D) Sites on RNA that are the target of a selective RNase, used to suppress the expression of genes selectively.
E) Hot spots for homologous recombination, used to introduce genes into the genome by homologous recombination.