9. What is the minimum number of square root symbols that must appear in the expression $\sqrt{\cdots \sqrt{\sqrt{123.456 .789}}}$ so that the result is less than 2?
(A) 5
(B) 6
(C) 7
(D) 8
(E) 9.
9. The answer is (A). Since, for non-negative numbers, $\sqrt{a}10^{3}$, it is found that $2^{2^{5}}=2^{32}>10^{9}=1,000,000,000>123,456,789$. It is also observed that 4 root extractions are not enough, as $2^{16}=65536$.