1.   Civic activity, a potential substitute for spending, has declined.

2.   Hemopure was still in clinical trials, a point at which many other potential substitutes had failed.

3.   Starting that year, each school and school district became responsible for maintaining its own list of potential substitutes.

4.   The full-employment economy, where potential substitute teachers might make better money flipping burgers, is not helping.

5.   Daniel Saric, a potential substitute, also was not on the roster.

6.   It was seen as a potential substitute to alcohol, which is abused widely.