All of the following are types of microorganisms, except 1.bacteria 2.virus 3.parasitic worms 3.rickettsias

All the choices are microorganisms apart from parastic worms. Microorganisms are microscopic organisms that can be single celled or multi-celled. On the other hand a parasitic worm is a disease causing  organism that is found in humans. Some of these parasitic worms can be seen with the naked aye and hence are not microscopic.

The answer is observations and interpreting.