Which of the following is true about a line and column combo chart?

a$.$ It is often useful to display a secondary $y-$axis when using a line and column combo chart.

b$.$ You need to select four continous measures to populate a line and column combo chart with data.

c$.$ A line and column combo chart is ideal for displaying the correlation between two continous fields.

d$.$ A line and column chart has no $x-$axis.