In the passage given below, 10 words have been omitted and blanks have been numbered. Choose from sets of four words against corresponding numbers the one that would fill the blank accurately and appropriately.
A modern example of the process of evolution by natural selection in action is provided by the peppered moth. The moth is (41) pale in colour, a mottled grey which (42) the moth to settle, wings outstretched, (43) the bark of lichen covered trees and (44) unnoticed. It can thus save itself from many (45) birds. However, many years ago some British (46) found that there does exist a second (47) of this Moth, with dark sooty wings. Research has (48) established that both belong to the (49) species, but the dark moth lives in (50) surroundings, where the trunks of the trees on which they live are dark with industrial grime.