The drugs tend to cause drowsiness.

　　這些藥常常使人昏昏欲睡。

　　The cause of the fire is not yet known.

　　火災的原因尚不清楚。

　　The immediate cause of death is unknown.

　　造成死亡的直接原因不明。

　　Unemployment is a major cause of poverty.

　　失業(yè)是貧困的主要原因。