exercise作為 體育鍛煉解釋是為不可數名詞。再如：
Take exercise in the open air. 在戶外做運動. 來自《簡明英漢詞典》
Take exercise if you're out of shape. 身體不好就要鍛煉. 來自《簡明英漢詞典》
People in sedentary jobs need to take exercise. 工作上要久坐的人需要做運動. 來自《簡明英漢詞典》
exercise 作為練習;習題解釋時， 為可數名詞。
Try working through the opening exercises in this chapter... 做壹做本章節的開篇習題。
He took up piano lessons, combining standard classical exercises with his own attempts at Gershwin. 他上鋼琴課，壹邊進行標準的經典作品的練習，壹邊自己嘗試練習格什溫的作品。