Which assumption is applied when a bookkeeper uses US dollars without accounting for currency value changes?

The Monetary Unit Assumption is the correct choice because it pertains to the practice of recording financial transactions in a stable currency, such as US dollars, without adjusting for changes in currency value over time. This assumption allows bookkeepers to use a consistent unit of measurement (the dollar, in this case) when preparing financial statements, facilitating easier comparison and analysis of financial performance over periods. It simplifies recordkeeping by ignoring potential fluctuations in value due to inflation or other economic factors, which can complicate financial reporting.

This assumption is foundational in accounting, providing a basis for how transactions are quantified and reported, enabling businesses to track their financial activities without the complexities of currency depreciation or appreciation. Other principles mentioned do serve distinct purposes in accounting but do not specifically address the use of currency and its value fluctuations.