Professor Johnson is said _____ some significant advance in his research in the past years.
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Our（）sensitivitydecreaseswithage.Byage60，mostpeoplehavelost40percentoftheirabilitytosmelland50percentoftheirtastebuds.
Henoticedthehelicopterhoveringoverthefield.Thentohisastonishment,hesawaropeladder_____outandthreemenclimbingdownit.
Itisimperativethatstudents_____theirtermpapersontime.