We must take care of all living species on earth.

1. All living species on earth must be taken care of by us
2. All living species on earth must take care of by us
3. All living species on Earth had been taken care of by us
4. All living species on earth will be taken care of by us
5. None of the above

The given sentence contains one of the Model verbs (Model Verb = will, shall, can, may, might, could, might, must, would). It is an inactive voice.

Rule :
Subject + Model verb + be + V3 + Optional Objects.