One of the Duolingo English Test's recurring items shows a grid of words and asks which are real English words. The rest are invented — built to look English, with English spelling patterns and plausible endings.
Why it matters more than it looks. The test is adaptive and these items come round often, so your answers here help set the difficulty of everything that follows. A weak start pulls the whole test down into a range where you cannot demonstrate what you know.
Selecting a fake costs you. The scoring penalises choosing invented words, so this is not a "select everything that might be real" item. If you do not recognise a word, leave it.
How the fakes are built. They are morphologically plausible: a real prefix, a real suffix, a stem that does not exist — *fromption*, *disparate* against *disparant*, *observal* for *observation*. If you find yourself constructing a meaning for a word rather than recalling one, that is the signal. A word you know arrives with a meaning attached; a word you are reasoning towards is usually a fake.
Trust the first instant. These items are timed tightly and recognition is fast by nature. Deliberating rarely converts a "maybe" into a "yes" correctly.
How to prepare for it, which is not by cramming lists. Wide reading is the only thing that works, because recognition depends on having met the word in use. Academic articles, quality journalism, and the vocabulary of your own subject in English. Learning definitions from a list builds exactly the reasoned, constructed knowledge that these items are designed to catch out.
And the parallel listening item. The test does the same thing with audio: real words and invented ones read aloud. Same rule — select what you recognise, leave what you are reasoning about.