let them loose, is the word" loose" an adj, adv. or v.?
There is a vocabulary question: By infecting animals and letting them loose in burrows... Which word can replace the word "letting"? （a) allowing (b) leaving (c) introducing (d) turning
The correct answer is (d). And I am confused about the answer, why we should choose (d) over (a)? What's the function of the word "loose" in this sentence?