FISA, the Foreign Intelligence Surveillance Court (FISA) Has Performed Oversight

FISA, the Foreign Intelligence Surveillance Court (FISA) has performed oversight on the NSA. How has this affected the NSA's ability to collect data?

A) FISA have kept the NSA from gathering the data that they need.
B) They have been unable to slow it down much in its efforts to snoop.
C) FISA allows them to gather information on known terrorists and seriously limits anything else.
D) The NSA has only been allowed to snoop where it has been necessary.