Final answer:
A heterotroph obtains energy for cellular respiration from consuming organic compounds like grass, not from light or inorganic substances.
Step-by-step explanation:
A heterotroph might obtain energy for cellular respiration primarily through the consumption of organic compounds. Therefore, among the provided options, a heterotroph would obtain energy for cellular respiration from B) grass, which is an organic substance that can provide the necessary carbohydrates for the energy production process. Heterotrophs cannot utilize light directly for energy (as autotrophs do in photosynthesis) nor can they use inorganic substances for energy as chemolithoautotrophs do.