1、The causative factor of the disease is still unknown.
这种疾病的促发因素仍然未知。

2、The causative agent of the infection is believed to be a certain bacteria.
传染的原因被认为是某种细菌。

3、Excessive use of electronic devices is causative of eye strain.
过度使用电子设备是导致眼部疲劳的原因。