Studies of healthy people indicate that functioning of the human body remains essentially constant until a. after age 70. b. after age 60. c. after age 50. d. age 40.

The correct answer that would best complete the given statement above would be option A. Studies of healthy people indicate that functioning of the human body remains essentially constant until the age of 70 or about 70 years old. Hope this answers your question. 

Your answer is going to be b.

4) repetitive change