For the following processes, is the work done by the system (defined as the expanding or contracting gas) on the environment positive or negative?

(a) Expansion of the burned gasoline–air mixture in the cylinder of an automobile engine;

(b) Opening a bottle of champagne;

(c) Filling a scuba tank with compressed air;

(d) Partial crumpling of a sealed, empty water bottle as you drive from the mountains down to sea level.