Two investments are plotted against time on the same axes. Which one gives a straight line graph?

1. Simple interest adds the same amount of interest in every year. 2. Adding a constant amount each year produces a straight line graph. 3. Compound interest adds a growing amount each year and produces an exponential graph. 4. Population growth and inflation both follow the compound pattern, so neither of those plots as a straight line. _Source: Siyavula Mathematics Grade 10 (Everything Maths, CC BY 4.0), Chapter 9: Finance and growth_