We can do a lot to stay healthy. we should eat a balanced diet.A. At a time B. In fact C.

问题补充：

We can do a lot to stay healthy., we should eat a balanced diet.

A. At a time B. In fact C. First of all

答案：

解析：介词辨析。A每次；B事实上；D首先；结合句意可知C正确。句意：为了保持健康，我们能做很多事情，首先，我们应该有平衡的饮食。