$$
\begin{array}{l}
A=\{2,0,1,7\}, \\
B=\{x \mid x=a b, a, b \in A\} .
\end{array}
$$

The number of elements in set $B$ is $\qquad$
$$
\begin{array}{l}
\text { I. 1.7. } \\
\text { It is easy to see that, } B=\{0,1,4,49,2,7,14\} \text {. }
\end{array}
$$

Therefore, $|B|=7$.