Before revision:  A major advancement in natural-language understanding has been the use of pre-trained token embeddings; BERT and other works have further shown that pre-trained contextual embeddingscan be extremely powerful and can be fine-tuned effectively for a variety of downstream supervised tasks .
After revision:  A major advancement in natural-language understanding has been the use of pre-trained contextual embeddings, such as BERT, which can be fine-tuned effectively for a variety of downstream supervised tasks .