5. A 1-year-old boy underwent cardiac surgery 4 days ago. He had no postoperative complication except persistent draining of left intercostal drainage, approximately 100 mL/day. Pleural analysis: cloudy yellowish fluid, pH 7.3, protein 3.0 g/dL(serum protein 3.5 g/dL, LDH 200 U/L (serum LDH 350 U/L), cell: WBC 1,500 cell/mm3, PMN 2%, mono 98%.Which of the following is the most likely presumptive diagnosis?