Match the following concepts with the correct definitions:

 1. $f$ is an onto function from ${\mathbb R}^3$ to ${\mathbb R}^3$
 2. $f$ is a one-to-one function from ${\mathbb R}^3$ to ${\mathbb R}^3$
 3. $f$ is a function from ${\mathbb R}^3$ to ${\mathbb R}^3$

A. For every $y\in {\mathbb R}^3$, there is a unique $x\in {\mathbb R}^3$ such that $f(x)=y$.
B. For every $x\in {\mathbb R}^3$, there is a $y\in {\mathbb R}^3$ such that $f(x)=y$.
C. For every $y \in {\mathbb R}^3$, there is at most one $x\in {\mathbb R}^3$ such that $f(x)=y$.
D. For every $y\in {\mathbb R}^3$, there is a $x\in {\mathbb R}^3$ such that $f(x)=y$.