Relate real numbers to complex numbers

Every real number a is also the complex number $a+0i$. But i is complex and not real. This completes both Teacher blanks: “subset” and $\mathbb R\subset\mathbb C$. In the source nesting, $\mathbb N\subset\mathbb Z\subset\mathbb Q\subset\mathbb R\subset\mathbb C$; the real numbers include both rational and irrational values.