A 30-year-old female developed fever and arthralgia after catching a cold for 2 months. She was hospitalized with generalized edema and oliguria for the past week. X-ray examination revealed pericardial and pleural effusion. Laboratory tests showed: urinary protein (+++), plasma albumin 24g/L, Hb 83g/L, reticulocyte count 0.20 (20%), platelets 60×10<sup>9</sup>/L, anti-dsDNA antibody (+), erythrocyte sedimentation rate (ESR) 110mm/1h. One week later, the patient developed melena with occult blood (++++). The preferred treatment is: