Which one statement is true about the main learning objective used to train the language transformer models?

Question $3$Select one:

The transformer model has been trained to predict the next word giving the left context in a sentence.

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The transformer model has been trained to predict the context words around a given central word.

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The transformer model has been trained to predict the topic of each sentence in a document.

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The transformer model receives the bag of word embeddings and tries to put words in correct order.