1、Do they know what caused the fire?
2、It is not known what causes the disease.
3、The cause of the fire is not yet known.
Do they know what caused the fire?
他们知道引起这场火灾的原因吗？
It is not known what causes the disease.
这种病的起因不明。
Police are trying to establish the cause of death.
警方在设法确定死因。
