New nests were built by swallows every year.
New nests were built by swallows every year.
New nests were being built by swallows every year.
New nests were being built by swallows every year.
New nests are built by swallows every year.
New nests are built by swallows every year.
New nests is being built by swallows every year.
New nests is being built by swallows every year.
Correct Answer:
New nests are built by swallows every year.
New nests are built by swallows every year.