- Conclusion for scenario (a): There is a correlation and possible causation between the variables.
- Conclusion for scenario (b): There is no correlation between the variables.
- Conclusion for scenario (c): There is no correlation between the variables.
Thus, the answers are:
- (a) Correlation exists, causation unknown.
- (b) No correlation.
- (c) No correlation.
The final answers are:
\[
\boxed{\text{(a) Correlation exists, causation unknown; (b) No correlation; (c) No correlation.}}
\]