Eдинственное число (множнственное число):
1. The man (men) looked at the shelf (shelves).
2. The leaf (leaves) fell from the tree (trees).
3. A bird (the birds) sang on the branch (branches) of a tree (the trees).
4. That lady (ladies) gave the girl (girls) a key (the keys).
5. The child (children) saw a sheep (the sheep) in the field (fields).
6. The ox (oxen) ate the grass.