Title: Hydrogen.
Question: What industries can you find these applications?

Title: Economy of Greece.
Question: What prompted the allegation of Greece's covering up its budget deficit?

Title: Madonna (entertainer).
Question: Who holds the record for the most number 1 hits?

Title: Ashkenazi Jews.
Question:
A 2013 study estimates that what percentage of Ashkenazi maternal ancestry comes from women of undetermined origins?