______ you are ready, you can start.

• A. Once
• B. When
• C. If
• D. Unless

Answer: (A)

This sentence hinges on using a time conjunction to show that starting depends on reaching a state first. Once marks that moment: as soon as you are ready, you can start. It conveys a clear sequence where readiness is the trigger for starting.

When you are ready would also be acceptable and natural, but Once adds a stronger sense of a definite point at which starting is allowed. If you are ready would frame it more as a condition you might meet, rather than the moment you reach readiness. Unless wouldn’t fit here, since it would imply a negative condition (you won’t start unless you’re not ready), which changes the meaning.