|Question 2Verbal

Source Texts

Text
Because cyanobacteria and other microphytobenthos (MPB)—microscopic organisms inhabiting tidal flats—are consumed by mussels as well as by certain shorebirds and fish, MPB are ______ estuary ecosystems. Decreased MPB abundance, which may be caused by environmental stressors, thus has a direct, negative impact on coastal food webs.
Which choice completes the text with the most logical and precise word or phrase?
imperative for
A
emblematic of
B
subordinate to
C
interchangeable with
D