Answer:
Option C, The Euglena cells, which are both autotrophic and heterotrophic, remain alive even in the absence of sunlight because
they can feed upon the organic material present in the pond water.
Step-by-step explanation:
Euglena is a special organism as it possesses the characteristics of both autotrophic and heterotrophic species. In the presence of light the chloroplast with in the Euglena entraps energy from sun and use it in the process of photosynthesis to make its own food. But in the absence of sunlight , euglena is capable to absorb food through its cell membrane and thus in this way they can also behave as heterotroph.
Thus Euglena placed in darkness in a vessel containing pond water will survive.