A colon.
Punctuation goes after the bracket.
A period would go inside parentheses to finish a complete sentence, but you always need sentence-ending punctuation outside of the parentheses.
A colon typically comes before a list or explanation. It is placed at the end of the sentence, followed by a single space and then the first item or explanation.
The comma typically goes before the parentheses if it is part of the main sentence. If the parentheses contain a complete sentence, the period or other punctuation mark will typically go inside the parentheses.
Punctuation is a feature of sentence structure. There is no word that must take any particular punctuation, and no word that cannot take any particular punctuation.
The correct punctuation for that sentence would be: "They all sang 'Happy Birthday' before she cut the cake." This includes putting 'Happy Birthday' in quotation marks and ending the sentence with a period.
Parentheses are placed at the end of a sentence before the final punctuation mark. If the entire sentence is within the parentheses, the period goes inside the closing parenthesis. For example: "He bought apples (which were on sale)." If the parentheses contain a complete sentence, the period should be placed inside the closing parentheses.
Comma's are the hardest punctuation mark to place in a sentence. A comma can be placed after instead at the beginning of a sentence if the sentence is a continuation of the subject in the one before it.
You can end a quote with a quotation mark. If the quote continues in the same paragraph, a comma is typically placed before the closing quotation mark. If the quote is a complete sentence, the ending punctuation (like a period or question mark) comes before the closing quotation mark.
A punctuation mark is put at the end of a sentence to denote the conclusion of an idea. The punctuation mark used here is mainly a period. However, if you use a question mark at the end of a sentence, then it is used to denote that the material before the question mark was a question. An exclamation mark is used to add emphasis to the before-stated material.
The footnote is inserted between the second and third word of the sentance. This is official chicago style, not MLA.
No it is not a complete sentence on its own. It is because there should be something before Therefore.