21.   For both sides, land has been a constant source of intertribal tension.

22.   For families living in Boston suburbs, ensuring that their au pairs get to and from downtown safely is a constant source of anxiety.

23.   He said most Internet technologies are a constant source of aggravation because they are new and untested.

24.   If one is messy and the other neat, for example, tidiness can be a constant source of conflict.

25.   I live near the Hudson River, and it is a constant source of delight.

26.   If you provide your cat with a constant source of food, he will be less likely to work for treats.

27.   It was a constant source of frustration for Yates as he watched Jarrett and Parrott flex their muscles while his other car scrambled.

28.   Many other pet owners are swearing profusely because their animals were a constant source of irritation.

29.   My lower back and hips have become a constant source of concern over time.

30.   Owner Jim Murphy said the billboard has been a constant source of conversation for his customers since it went up two weeks ago.