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had been mastering
  • past perfect progressive of master.

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

The Agency was still smaller than its Russian counterpart, and its agents had to train hard to learn the techniques of spycraft—which Soviet operatives had been mastering for decades.

From "Spies: The Secret Showdown Between America and Russia" by Marc Favreau

He had been reading up; he had been seeing distinguished confreres; he had been mastering the subject to the last dot, and was panting to begin.

From The Motormaniacs by Osbourne, Lloyd