a$.$ It lists the HTML$5$ code document that corresponds to the body$\}\}\}$ in the header.handlebars.

b$.$ It specifies a partial Handlebars file that should be included in this location when the page is requested.

c$.$ It is used by Handlebars to indicate that it should incorporate other Handlebars files.

d$.$ It is used by Handlebars to mark where in the layout it should include the body code.