What is the tournament when 2007 is WTA Premier 5 tournaments?
CREATE TABLE "single_performance_statistics" (
  "tournament" text,
  "2007" text,
  "2008" text,
  "2009" text,
  "2010" text,
  "2011" text,
  "2012" text
);
SELECT "tournament" FROM "single_performance_statistics" WHERE "2007"='wta premier 5 tournaments';