Properties that separate Rational Numbers from Reals, Rationals from Complex and Reals from Complex(First-Order Logic)

Question

I am given 3 $L_{ring}-Structures\; Q=(\mathbb{Q},0,1,+,\cdot)\;R=(\mathbb{R},0,1,+,\cdot)\;C=(\mathbb{C},0,1,+,\cdot)$, and tasked with finding a $L_{Ring}\; Sentence\; \varphi$ such that $M\models\varphi\;and\;M^{a}\not\models\varphi$(or vice-versa) for each pair of $M,M^{a}\in\{Q,R,C\},\;M\neq M^{a}$. I am having trouble turning properties that define the difference between $\mathbb{R},\mathbb{Q},\mathbb{C}$ into $L_{ring}$ sentences in first order logic.