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The desk which was stained was antique.
→ Reduced: The stained desk was antique.
The elephant which was born in captivity was set free.
→ Reduced: The elephant born in captivity was set free.
The dog that is lying on the floor won't get up.
→ Reduced: The dog lying on the floor won't get up.
My question is that: Can "The man who is eating is my dad." be reduced to "The eating man is my dad."?