take exercise 做体操，做健身活动；锻炼
exercise作为 体育锻炼解释是为不可数名词。再如：
Take exercise in the open air. 在户外做运动. 来自《简明英汉词典》
Take exercise if you're out of shape. 身体不好就要锻炼. 来自《简明英汉词典》
People in sedentary jobs need to take exercise. 工作上要久坐的人需要做运动. 来自《简明英汉词典》
exercise 作为练习;习题解释时， 为可数名词。
Try working through the opening exercises in this chapter... 做一做本章节的开篇习题。
He took up piano lessons, combining standard classical exercises with his own attempts at Gershwin. 他上钢琴课，一边进行标准的经典作品的练习，一边自己尝试练习格什温的作品。