In this task you are given a sentence. You must judge whether subject of the main clause is singular or plural. Label the instances as "Singular" or "Plural" based on your judgment.
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Question: The man-made chemical polonium leaks from the engines by tiny droplets.

Answer: Singular

Question: Her garage was behind it ; then there were two more houses stuck back there on the left.

Answer: Singular

Question: Great cliffs and undulating hills rose on either side of the river, so thickly forested that the underlying stone was nearly invisible.

Answer:
Plural