Englishfor English speakers
challenge
Noun
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A challenge is something difficult that you want or have to do.
Many churches overseas are struggling to meet the AIDS challenge.
After 25 years in the same job, this move will allow me to take on new challenges.
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A challenge is an offer to compete or fight.
The president issued a challenge to his critics to appear in a public debate.
challenge
Verb
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If you challenge somebody, you give them something very difficult to do.
The job challenges his computer skills.
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If you challenge somebody, you offer to compete or fight.
He challenged me to a game of chess.
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.
the
Determiner
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Used, instead of a, to reference something specific, already known to exist.
Compare "I read a book." and "I read the book."
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Used with a stress, to show that the word following is special.
Are you the John Smith that I went to school with?
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Used with an adjective that acts like a noun to mean all of the people concerned
The poor are always with us.
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Used with superlatives forms of adjectives and adverbs.
You are the best.
answer
Noun
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An answer is something that someone says after another person asks (says) a question.
The answer to your question is "no".
Question: "How old are you?"
Answer: "I'm 12 years old."
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An answer is the solution to something.
I found the answer to the mathematics exercise immediately.
answer
Verb
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To respond.
He answers all my questions.
system
Noun
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A group of things that work together; a way of doing something.
This coloured paper is part of my system for keeping lists of people.