It remains ______ whether he will pass the exam this time.
How the fire in the dancing hall started _________ a mystery.
Please don’t try to back out _____ everything has been arranged.
Simon is very regretful. If he had been more careful, he _____ such a big mistake.
______ by jeep, we visited a number of cities in South China.
Zheng He had over 300 ships, _______ some were over 150 meters long and could carry up to 1,000 people.