## When is it appropriate to use an R Line Graph with multiple lines?

a) When comparing trends across multiple variables over time

b) When displaying the distribution of a single variable

c) When comparing discrete categories

d) When illustrating proportions of a whole

### Answer:

a) When comparing trends across multiple variables over time

### Explanation:

It is appropriate to use an R line graph with multiple lines when comparing trends across multiple variables over time. Multiple lines on the same graph allow for a direct comparison of how different variables change relative to each other, making it easy to identify patterns, correlations, or divergences in trends.

```
# Example of a line graph with multiple lines
time <- c(1, 2, 3, 4, 5)
series1 <- c(10, 20, 30, 40, 50)
series2 <- c(15, 25, 20, 35, 45)
plot(time, series1, type = "o", col = "blue", xlab = "Time", ylab = "Values", main = "Multi-Line Graph Example")
lines(time, series2, type = "o", col = "red")
```

In this example, a line graph with two lines is used to compare two series of data over time. The blue and red lines represent different datasets, allowing for easy comparison of their respective trends. This type of graph is particularly useful in time series analysis or when you need to compare the performance of multiple metrics or variables simultaneously.