What is the necessary first step to solve the problem $\frac{2}{5} + \frac{3}{10}$?

Convert $\frac{2}{5}$ to an equivalent fraction with a denominator of 10.

Convert $\frac{3}{10}$ to an equivalent fraction with a denominator of 5.

Which statement best explains why we need a common denominator to add fractions?

To make the numerators smaller.

Because the fractions must represent the same kind of unit or piece size.

To ensure the sum is always less than 1.

Because addition only works with even numbers in the denominator.