In the Formula =SUM('San Francisco'!A6:D6), What Do the Single Quotation

Multiple Choice

In the formula =SUM('San Francisco'!A6:D6) , what do the single quotation marks around the worksheet reference indicate?

A) The sheet name includes a space.
B) The cells are in another workbook.
C) The cells are in another worksheet.
D) San Francisco is the name of a table column.