When the Supreme Court Declared That President Nixon Had to Follow

When the Supreme Court declared that President Nixon had to follow congressional demands to turn over secretly recorded White House tapes about the Watergate scandal, it might have seemed like a major loss for the White House.The president resigned shortly after the ruling was handed down, after all. While it was a loss for the Nixon White House, the Court's ruling was favorable over the long term for the presidency as an institution because the Court:

A) established that presidents could secretly record conversations in all executive offices, without the knowledge of others involved, including foreign dignitaries.
B) recognized as valid the idea that presidents could invoke "executive privilege" in refusing to turn over to Congress conversations with advisers.
C) recognized that presidents could constitutionally refuse to accede to congressional demands to turn over documents and conversations related to national security, if not domestic affairs.
D) asserted that it could allow a limited invocation of executive privilege, even in situations involving alleged illegal presidential behavior, to block congressional access to presidential documents.