A:a=1

The equation \( a : a = 1 \) represents the proportion of \( a \) to itself. Since any non-zero number divided by itself equals 1, this is true for all \( a \neq 0 \). To elaborate: \[ \frac{a}{a} = 1 \quad \text{for } a \neq 0 \] If \( a = 0 \), the expression is undefined because division by zero is not permitted. If you have any more questions or need clarification on related topics, feel free to ask!