a period of history a procedure a process
an agreement the reason a region

1. My teacher said I failed my assignment is that I failed to proofread it.
2. Catharsis is repressed emotions are brought to consciousness.
3. The tundra is the subsoil is permanently frozen.
4. The Dark Ages was little was documented.
5. France and Germany reached their citizens could cross shared borders without a passport.
6. Keyhole surgery is the surgeon makes two or three small incisions.