|Question 11Verbal

Source Texts

Text
The fungus Paxillus atrotomentosus, commonly referred to as velvet roll-rim, is known to establish ectomycorrhizal bonds with certain alder tree species; in many cases, such symbiotic relationships, wherein fungal hyphae make contact with the alder'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?
forming
A
form
B
to form
C
having formed
D