What are 3 things that can't be seen but can be touched?

On a floor there are several 1-4 mm elongated drops leading away from a body lying in a pool of blood. the the forward wall there is a sigzag pattern and on the walls to the right side there is a linear patter

The kind of fertilization found in the majority of aquatic animals is (internal or external) fertilization.

Anne, an intern in a microbiology lab, was observing the characteristics of various specimens of protists. match each specimen to the category of protist to which it belongs.