Answer:
C. extremely small.
Step-by-step explanation:
The word "infinitesimal" means "minute, tiny, extremely small," even to the extreme of being considered uncountable or difficult to be considered. The word is used to describe or refer to things that are small, more than the normal small.
In the given excerpt from the short story "The Revolt of 'Mother'," by Mary E. Wilkins Freeman, the writer used the word "infinitesimal" to refer to the house. And based on how it is used to talk about the house, we can infer that it meant the house was "extremely small", even comparing it to "the little boxes under the barn eaves" that were for the doves.
Thus, the correct answer is option C.