Please help with these concept questions off my finance study guide.

1. In NPV profile what does the cross-over rate imply about the NPVs of two exclusive projects?

2. What determines that a cost is considered sunk?

3. What determines that a seemingly non-cost should be considered an opportunity cost?

4. Why is depreciation expense added to the other components of free cash flows?

5. What are the various types of NPV stress testing techniques and how they are different from one another?