1.   It was a continual source of irritation to Lewis that Adam did not show more respect and deference to Hilbert.

2.   Seating arrangements at conferences, forms of address and other issues of this kind remained a continual source of potential difficulty.

3.   The continual source of our strength was our mutual trust and respect.

4.   A continual source of emotional support is a group called the Team Mothers.

5.   This was a continual source of amazement to me.