_____ for a long time, but he tried his best to catch up with hi

_____ for a long time, but he tried his best to catch up with his classmates.
A、Having been ill
B、Being ill
C、Though he was ill
D、He was ill
【正确答案】：D
【题目解析】：有but 连接词，因此前后应为两个完整的句子，D选项正确。C选项 though 和 but 不能连用，因此不选