No convincing explanation has as yet been found.
A convincing explanation hasn't been found.
A convincing explanation was found.
Two trains are boarding at a new train station.
Two people are sitting next to each other on the subway.
It is possible that, if Greenspan did not respond soon enough, the economy would be negatively effected.
The torches were not lit.
A lady with a large black bag is walking in the rain.
The Young Adventurers were told that they would be completely safe.