The ______ is used to summarize the correlations between a set of variables:

A) scatterplot
B) correlation
C) correlation matrix
D) scatterplot matrix

A correlation matrix is used to summarize the correlations between a set of variables. It shows the correlation coefficient between each pair of variables in a matrix format, which helps in identifying the strength and direction of relationships between variables. Scatterplots and scatterplot matrices can show the relationship between two or more variables, but do not summarize the correlations between multiple variables. Correlation is a statistical measure of the association between two variables, but it does not summarize the correlations between a set of variables.