We may find that learning a foreign language does not have to be________learning our mother tongue,but can in fact be twice ________.
This problem may lead to more serious ones if _____ unsolved.
What a fast learner he was! He_____ a lot of French when he lived with the native.
—Does John serve in the army?—No, but he________in the army for 8 years.
He was working on a new book ________ I went to see him.
Not until the motorbike looked almost new repairing and cleaning it.