The weeds are followed by the city's most prolific exotic species, the Chinese ailanthus tree. Even with 8 million
people around, ailanthus-otherwise innocently known as
the tree-of-heaven-are implacable invaders capable of
rooting in tiny chinks in subway tunnels, unnoticed until
their spreading leaf canopies start poking from sidewalk
grates. With no one to yank their seedlings, within five
years powerful ailanthus roots are heaving up sidewalks
and wreaking havoc in sewers.
Which statement best explains how irony is used in the passage ?

The correct answer is D. Weed tree that wreaks havoc on the environment is referred to favorably as the "tree-of-heaven."

Explanation:

Irony occurs when the outcome in a situation is not the one expected or words have an opposite meaning to the literal meaning. In the excerpt, there is irony because the three known as the "tree-of-heaven" in China is an invasive and harmful species. This can be seen in "implacable invaders capable of rooting in tiny chinks in subway tunnels" and in "heaving up sidewalks and wreaking havoc in sewers" that shows the power the tree has to invade spaces and destroy structures despite the name suggests the tree is positive. This means there is an incongruence between the expectations about the tree and the reality. Thus, the statement that explains irony is statement D.

the type of supporting detail is fact!