Studying the deepest parts of the ocean is a daunting task. Humans cannot survive the crushing pressure, freezing temperatures, and lack of light that characterize what's called the “abyssal zone”. Specially designed submarines and robots can explore this realm, but ______ highly expensive and limited by technical challenges.

Question

Studying the deepest parts of the ocean is a daunting task. Humans cannot survive the crushing pressure, freezing temperatures, and lack of light that characterize what's called the “abyssal zone”. Specially designed submarines and robots can explore this realm, but ______ highly expensive and limited by technical challenges.
Which choice completes the text so that it conforms to the conventions of Standard English?
Choose 1 answer:
Choose 1 answer:
(Choice A)   it is 
A
it is
(Choice B)   they are 
B
they are
(Choice C)   we are 
C
we are
(Choice D)   this is 
D
this is

GPT 3.5 · Answer

A. it is