A shift in thought can be indicated by the use of C. an em dash.
An em dash is used to set of an interruption that is closely relevant to the sentence but is not grammatically part of it. These set of interruptions can be found in a list, illustration, restatement, shift in thought or tone, summary, or dramatic point.
Semicolon (;) is used to connect independent clauses.
Ellipses (. . .) are used to indicate that material is missing in the sentence or passage.