Final answer:
The correct answer is 'aes()'. The aes() function in ggplot is used to define the mappings of variables to visual representations of data. It is a crucial function in creating graphics using ggplot.
Step-by-step explanation:
The correct answer is b. aes().
The aes() function in ggplot is used to define the mappings of variables to visual representations of data. It stands for aesthetics and is a crucial function in creating graphics using ggplot. It allows you to specify how variables should be represented visually, such as mapping a variable to the x or y-axis, color, shape, or size.
For example, if you have a dataset with variables 'x' and 'y', you can use the aes() function to map 'x' to the x-axis and 'y' to the y-axis in a scatter plot.