Example of Representing Masked Spans with Sentinel Tokens

A language model is given the input sentence: 'The new algorithm significantly improves performance on the benchmark.' In this instance, the consecutive words 'significantly improves' and 'on the benchmark' are both masked for a training task. How would this input be correctly represented if the modeling approach replaces each contiguous masked span with a single, unique placeholder token?

In a text processing approach where a single, unique placeholder replaces a span of one or more masked words, it is permissible to use the same placeholder (e.g., [X]) to represent two different, non-overlapping masked spans within the same input sentence.

Consider the following input sequence where several consecutive tokens have been masked: The model was trained [MASK] [MASK] a large dataset and then [MASK] [MASK] [MASK] on a specific task. Rewrite this sequence by replacing each contiguous span of masked tokens with a single, unique sentinel token, starting with [X]. Your answer should be the complete, rewritten sequence: ____