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.
Body Facts
A person produces 1.5 litres (2.6 pints) of spit (saliva) every day and swallows almost all of it.
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