The Tiwi geothermal power plant in the Philippines provides a reliable source of renewable energy, yet geothermal plants supply only around 10.1% of the Philippines’ electricity. Indeed, the necessary combination of naturally occurring geological and hydrological features—accessible underground reservoirs, sufficiently high subterranean temperatures, and fractured rocks—__________ relatively rare, effectively limiting the Philippines’ development of new geothermal energy infrastructure.
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Verbal·Standard English Conventions·Form, Structure, and Sense
hardWhich choice completes the text so that it conforms to the conventions of Standard English?
A
proving
B
have proved
C
has proved
D
are proving