|Question 22Verbal

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Vanadium 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 vanadium 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?
To date,
A
In doing so,
B
Finally,
C
Similarly,
D