Complete each statement.
a. To simplify a fraction, we remove factors equal to in the form of $\frac{2}{2}, \frac{3}{3},$ or $\frac{4}{4},$ and so on.
b. To build a fraction, we multiply it by $\quad$ in the form of $\frac{2}{2}, \frac{3}{3}$
or $\frac{4}{4},$ and so on.