Answer: C): when showing trends
Step-by-step explanation:
A Line graph connects different points such that it appears as a line. For this reason it is very useful in showing the trend in the movement of values overtime.
When plotting line graphs the independent variable for example 'months' is usually put on the x-axis and a dependent variable such as 'temperature' will be on the y-axis.
When plotted, the line will be able to show just how things have changed overtime such that the change is quite easy to see through the movement of the line.