Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.
One example: Context: Architecturally, the school has a Catholic character. Atop the Main Building's gold dome is a golden statue of the Virgin Mary. Immediately in front of the Main Building and facing it, is a copper statue of Christ with arms upraised with the legend 'Venite Ad Me Omnes'. Next to the Main Building is the Basilica of the Sacred Heart. Immediately behind the basilica is the Grotto, a Marian place of prayer and reflection. It is a replica of the grotto at Lourdes, France where the Virgin Mary reputedly appeared to Saint Bernadette Soubirous in 1858. At the end of the main drive (and in a direct line that connects through 3 statues and the Gold Dome), is a simple, modern stone statue of Mary.
Question: To whom did the Virgin Mary allegedly appear in 1858 in Lourdes France?
Solution is here: Saint Bernadette Soubirous
Explanation: This is the correct answer. Because the question is asking for the name of the person and following sentence from the passage answers it: It is a replica of the grotto at Lourdes, France where the Virgin Mary reputedly appeared to Saint Bernadette Soubirous in 1858.

Now, solve this: Context: The first step in the management of restless legs syndrome (RLS) is to identify, and if possible to treat any condition which might cause or worsen RLS, such as iron deficiency or some drug treatments. The patients suffering from RLS should be prompted to keep a healthy sleep schedule. Drug treatment should be restricted to patients with a clear clinical diagnosis, decided on an individual basis, when the clinical impact is serious. Four drug classes are central to the treatment of RLS: dopaminergic agents, some antiepileptics, opioids, and benzodiazepines. Dopaminergic agonists are the treatment of choice, especially when daily treatment is indicated, or if the symptoms are severe. Two dopaminergic agonists are licensed in France for the treatment of RLS: ropinirole (Adartrel) and pramipexole (Sifrol). After initiation of treatment, the patients should benefit from a regular follow-up in order to evaluate the efficacy of treatment and to identify possible side-effects. Special care should be given to the detection of augmentation, a phenomenon characterized by a paradoxical worsening of the symptoms with treatment. Some particular conditions, such as RLS comorbid with renal insufficiency, during pregnancy, and in the child are discussed.
Question: Which deficiency is the cause of restless leg syndrome?
Solution:
iron