A two-month-old infant is brought to the hospital emergency with marked respiratory distress. On examination, the infant has cyanosis and bilateral crepitations. Hea rate is 180/min, respiratory rate 56/min and the liver span 7.5 cm. The child has had repeated episodes of fever, cough and respiratory distress since the time of bih. Cardiovascular examination reveals a grade III ejection systolic murmur in left parasternal area and the chest X-ray reveals cardiomegaly with a narrow base and plethoric lung fields. What is the most likely diagnosis ?