When a student adds a few drops of diluted picric acid to a paramecium slide, he observes that the paramecium releases some transparent spine-like projections to protect its body from the acid. what is the significance of these properties?

I believe the answer is The projections are trichocysts, released for the self-defense of the paramecium.
Trichocysts could be easily found in the pathway of the metabolic system. Even though scientists still haven't figured out the actual significant function of trichocysts,  Paramecium apparently can be extruded for anchorage during feeding.

Green pods should be the a, c, d.

Ithink the answer is maybe a