Which product innovation first allowed dictionaries to incorporate audio pronunciation guides for users?

Test your knowledge about how dictionaries have evolved through product innovation! Dictionaries might seem like static reference materials, but they've undergone fascinating transformations as products over time. From massive multi-volume tomes to pocket editions to digital platforms, dictionary makers have continuously innovated to meet changing consumer needs. This poll explores a pivotal moment in dictionary product development that revolutionized how we access language information.

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CD-ROM dictionary editions released in the 1990s
Cassette tape companions sold with print dictionaries in the 1980s
Vinyl record supplements included with academic dictionaries in the 1970s
Internet-based online dictionaries launched in the early 2000s