Which of the following is true of row groups that are defined in an HTML table?

a$.$ The thead element must appear first, followed by the tbody element, and finally the tfoot element.

b$.$ A table can contain only one thead and tfoot element but can have numerous tbody elements.

c$.$ A table can contain only one tbody element which is added between thead and tfoot element.

d$.$ The tbody appears before tfoot to allow the browser to render the body before receiving numerous of tfoot rows.