1. The problem involves understanding whether variables can have restrictions such as being non-negative and how to interpret graph cropping. 2. In many real-world scenarios, some variables cannot be negative (e.g., distance, time) because they represent quantities that do not make sense as negative values. 3. Other variables might be allowed to take negative values (e.g., temperature, velocity) depending on the context. 4. When graphing, cropping the graph starting from zero is not a strict rule; it depends on the scenario and the domain of the variables involved. 5. Always interpret each scenario individually to decide if variables have restrictions and how to display their graphs. 6. For example, if $x$ represents time, then $x \geq 0$; if $y$ represents temperature, $y$ can be negative or positive. 7. This understanding helps in correctly setting the domain and range when graphing functions or interpreting data.