A. is improving; takingB. has been improved; being takenC. improved; takenD. is improving;

问题补充：

A. is improving; taking

B. has been improved; being taken

C. improved; taken

D. is improving; have taken

答案：

(答案→)A. is improving; taking

B. has been improved; being taken

C. improved; taken

D. is improving; have taken

解析：他觉得每隔一天的长距离散步使自己的健康状况每天都在改善。owing to的to是介词，后面要加名词或动名词，而他散步，是主动的动作，故选A。