The answer should be A. building.
After doing research, i found the question and question choices you're looking for. "<span>In which sentence is the word singing a gerund?"
A. The hikers enjoyed the singing birds.
B. The birds are singing a cheerful song.
C. The birds’ singing filled the park.
D. The birds kept singing.
The correct answer is C.</span>
The answer for this answer is c
