A scientific theory is based on thorough observation and experimental evidence. Before the 1950s, genetic material was believed to be stored in proteins. However, in 1952, scientists experimentally proved that genetic materials are instead stored in nucleic acids, such as DNA and RNA. All the previous scientific knowledge about genes was still included in the new DNA gene theory, it was just modified to include that genes are coded by DNA and not proteins. Which of the following is true?
A.
Scientific theories are often modified but are rarely discarded.

B.
Scientific theories are always completely discarded when new research is done.

C.
A scientific theory can never be changed because scientists know everything.

D.
A scientific theory is based on opinion and changes based on who is doing the experiment