There are `x` trees and `y` parrots. If in each tree only one parrot is sitting, then one parrot remains without a tree. If in each tree, two parrots are sitting, then one tree remains without a parrot. Therefore, `x` and `y` are respectively (a) 3 and 4 (b) 4 and 5 (c) 5 and 6 (d) 6 and 7