To answer this question we need to analyze each available option:
A. Heterotroph. These organisms depend on an external organic source of energy to sustain themselves as is the case of animals.
B. Decomposer. These organisms as their name say decompose and obtain their energetic income from organic decaying matter as is the case of fungi.
C. Chemoautotroph. These organisms produce their own food source from chemical compounds that are inedible for any other organisms, that is to say, they obtain their energetic input from inorganic chemical compounds, therefore this is the correct answer.