.It was ______ the 19th century_____ heat was considered to be a form of energy.
. Mage is rather difficult to make friends with, but her friendship, _____ is truer than any other.
Only through experiences of trial and suffering _____, and success achieved.
Unless _____, the Minister wouldn't attend the welcome party.
We all feel puzzled why the students _____ the same mistakes repeatedly in exams.
To their relief, their students _____ escaped from the shaking building.