|Question 18Verbal

Source Texts

Text
The fungus Scleroderma citrinum, commonly referred to as common earthball, is known to establish ectomycorrhizal bonds with certain oak tree species; in many cases, such symbiotic relationships, wherein fungal hyphae make contact with the oak's root system,        extensive networks, which can be used to transport nutrients between trees.
Which choice completes the text so that it conforms to the conventions of Standard English?
to form
A
having formed
B
form
C
forming
D