What roles earned Meryl Streep an Oscar?

Meryl Streep has won three Oscars, for the following roles:

* Best Actress for her role as Sophie Zawistowski in Sophie's Choice (1982)

* Best Actress for her role as Miranda Priestly in The Devil Wears Prada (2006)

* Best Supporting Actress for her role as Margaret Thatcher in The Iron Lady (2012)