A person was dialing a telephone. He forgot the last three

A person was dialing a telephone. He forgot the last three digits of the six-digit telephone number but rembered that the number formed by the last three digits in the same order was a perfect square. What is the probability he dialed a right number?

(A) 1/32
(B) 1/46
(C) 1/49
(D) 1/36
(E) 1/18


Please explain.