In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.

Question: What is the main cause of functional urinary incontinence in the elderly?
Options: <1> Detrusor instability. <2> Obstruction due to fecalomas. <3> Laxity of the muscles of the pelvic floor. <4> Environmental barriers. <5> Urinary retention induced by medication.
4