1.   As you can imagine, this was a constant source of campus conflict at the time.

2.   Furthermore, the fact that the old person is alone, especially at night, is a constant source of anxiety.

3.   Her children were a constant source of worry.

4.   Her garden was a constant source of pleasure.

5.   His independent attitude was a constant source of friction with his boss.

6.   Sometimes a sympathetic friend can be a constant source of discouragement, all unknowingly.

7.   The advertising of the scheme and the consequent level of public awareness has been a constant source of concern.

8.   The heavy traffic is a constant source of irritation.

9.   The nearby water spigot became a constant source of fascination.

10.   The number of students who had killed themselves and their instructors was a constant source of anxiety.