|Question 22Verbal

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Barium is one of a variety of potentially useful trace elements contained in the chemical-rich brine that remains after seawater is purified through desalination. However, routine extraction of barium and other such elements from brine is not yet technologically or economically feasible. _____ most trace elements have only been extracted from seawater on an experimental basis.
Which choice completes the text with the most logical transition?
Finally,
A
Similarly,
B
In doing so,
C
To date,
D