Englishfor English speakers
den
Noun
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A den is a place where a wild animal lives.
The wolf went back to his den to sleep after a day of hunting.
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A den is a small cave in the side of a hill.
by
Preposition
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near or next to.
The mailbox is by the bus stop.
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at some time before (the given time).
Be back by ten o'clock!
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if something is done by somebody, it is done through their action
The matter was decided by the chairman.
The boat was swamped by the water.
He was protected by his body armour.
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if something is created by somebody, they are the creator, author, etc.
There are many well-known plays by William Shakespeare.
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shows how someone does something
I avoided the guards by moving only when they weren't looking.
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using the rules or logic of.
I sorted the items by category.
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with a change of. In this case, by shows how much something has changed.
Our stock is up by ten percent.
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shows how slowly, or how quickly, someone does something (used in the form "X by X" or "by Xs")
We went through the book page by page.
We crawled forward by inches.
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If you multiply mathx/math by mathy/math, you multiply mathx/math × mathy/math.
Five multiplied by seven is 35.
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If you divide mathx/math by mathy/math, you find how many mathy/maths are in mathx/math.
35 divided by seven is five.