Question: Which low income country has a series code of DT.DOD.DECT.CD? Name the country code of it.
SQL: SELECT T1.CountryCode FROM Country AS T1 INNER JOIN CountryNotes AS T2 ON T1.CountryCode = T2.Countrycode WHERE T1.IncomeGroup = 'Low income' AND T2.Seriescode = 'DT.DOD.DECT.CD'