$14 \cdot 7$ is used to select a positive integer $n$ not exceeding 100. If $n \leqslant 50$, the probability of selecting $n$ is $p$; if $n>50$, the probability of selecting $n$ is $3p$. The probability of selecting a perfect square is 
(A) 0.05.
(B) 0.065.
(C) 0.08.
(D) 0.09.
(E) 0.1.
(29th American High School Mathematics Examination, 1978)
[Solution] From the given condition $50 p+50 \cdot 3 p=1$, then $p=0.005$. Also, there are 7 perfect squares not exceeding 50, and 3 between 51 and 100. Therefore, the probability of selecting a perfect square is $7 p+3 \cdot 3 p=0.08$. Hence, the answer is $(C)$.