Englishfor English speakers
challenging
Adjective
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If something is challenging, it is not easy but it can be done.
For a longer, wilder and more challenging route, you can explore the beautiful mountains around Goatfell.
All actors will agree that Hamlet is a very challenging role.
of
Preposition
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Made using.
It is a house of cards.
identification
Noun
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Identification is the process of a thing by seeing it, hearing it, and/or touching it.
With finding new animals, the process of identification is a long and difficult one.
You have to show your identification card before entering.