How many three-digit positive integers are perfect squares?
(A) 23
(B) 22
(C) 21
(D) 20
(E) 19
We determine the smallest and largest three-digit perfect squares first.

Clearly, the smallest three-digit perfect square is $100=10^{2}$.

Now $\sqrt{1000} \approx 31.6$, so the largest perfect square less than 1000 is $31^{2}=961$ (since $31^{2}1000$ ).

Therefore, only the perfect squares between $10^{2}=100$ and $31^{2}=961$ have three digits, which means that exactly 22 three-digit positive integers are perfect squares.

ANSWER: (B)