ANT: Inefficacious, inoperative.
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KEY: Operose.
SYN: Onerous, laborious, burdensome, tedious, wearisome, toilsome.
ANT: Light, unburdensome, stimulating, refreshing.
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KEY: Opine.
SYN: Think, believe, conjecture, suppose, judge, surmise.
ANT: Know, ascertain, verify.
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