tv/ movies: John Denver & George Burns appeared together in what 1977 film?

Questions

as tough as _____?

Similesas dry as a _____?

Since Hindus don't eat beef, the Mcdonald's in New Delhi makes its burgers with what?

Since the beginning of the modern olympics, which are the only 2 countries to compete in them all (list alphabetically)?

Since Thomas Jefferson was a widower, who became unofficial first lady during his administration?