4. There are exactly 35 consecutive natural numbers whose integer parts of the arithmetic square roots are the same. Then this same integer is
(A) 17 ;
(B) 18 ;
(C) 35 ;
(D) 36 .
4. (A)

Let the smallest of these 35 consecutive natural numbers be $n^{2}$, and the largest be
$$
\begin{array}{ll} 
& (n+1)^{2}-1 . \\
\therefore \quad & (n+1)^{2}-n^{2}=35, \\
\text { i.e. } \quad 2 n+1=35, \\
\therefore \quad & n=17 .
\end{array}
$$