[An officer from European Union border agency Frontex holds the documentation of a migrant boarding a Turkish-flagged passenger boat, to be returned to Turkey, on the Greek island of Lesbos]The number of migrants arriving in Greece dropped 90 percent in April, EU border agency Frontex said on Friday, in a sign that a deal with Turkey to send back those who make the sea journey between the two countries is working. Frontex said 2,700 people arrived in Greece from Turkey in April, most of them from Syria, Pakistan, Afghanistan and Iraq, a 90 percent fall from March. Under the deal with Turkey, all migrants and refugees, including Syrians, who cross to Greece illegally across the sea are sent back.