|Question 2Verbal

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The discoverers of the minor planet 713 Luscinia named it after the animal genus that includes nightingales. Most of the recently discovered minor planets, however, are given only an identification number, largely due to there being over 500,000 such bodies known at present, which makes the already challenging task of finding a unique name for each nearly       .
Which choice completes the text with the most logical and precise word or phrase?
substantial
A
insurmountable
B
unnecessary
C
feasible
D