1. On top of indicates a position higher than the object.
Pattern: verb + on top of + noun
They put the blanket on top of the sheets, and the bedspread on top of the blanket.
I’m sure I left my keys on top of the desk.
2. Expression
to be on top of something—to be sure about one's knowledge or control of something Her son had a hard time learning math, but he is on top of it now.
Fact
During World War II, the very first bomb dropped on Berlin by the Allies killed the only elephant in the Berlin Zoo
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