An example of a rhetorical technique a candidate could use in an opening statement is?

“then” and “now” statements.

Explanation:

Rhetorical techniques are devices for the use of language to communicate effectively and persuasively. Depending on the speaker's purpose, different rhetorical techniques can be used in the opening statement.

As the question does not explain what kind of objective the speaker has with the speech, we can determine that a good rhetorical technique for an opening statement is the "then" and "now" statements, because this type of statement can be used as a basis for any discourse that wishes to appeal to logic, ethics or the public's emotions.

c) all of the above

serious tone and/or informal tone