Mr. Li is gaining _______. He has to do some exercises to lo

B

词义辨析。Weighty形容词，重的；weigh名词，权衡，称重；weight重量，砝码；fa脂肪，肥肉；heavy重物。句意：李先生正在长胖（增重）。他不得不来做练习减肥。故选B。