Which One of the Following Statements Best Describes What an Assumption

Multiple Choice

Which one of the following statements best describes what an assumption is?

A) These are the things that may restrict the options for the endeavor.  
B) The weather will always be hot in the summer and cool in the winter.
C) The project must be completed by December 18.
D) These are things that are believed to be true, but they have not yet been confirmed.