Assuming that this is referring to the same passage that was posted before with this question, the best option would be "<span>C. Fruit trees cannot grow fruit without birds and bees to sing to them."</span>
The correct answer is letter C: a complete subject.
The correct explanation would be that it is formed by the simple subject (the vertical farm) and a modifier which describes the simple subject (dubbed "The Dragonfly").
In order to identify a complete subject, you have to ask yourself who or what do the action: What is a remarkable building?
The answer is: The vertical farm dubbed "The Dragonfly" (complete subject)
