Official Solution:If in a six-digit integer \(n\), \(f(k)\) represents the value of the \(k_{th}\) digit from the leftmost digit, is \(n\) is divisible by 7? (For example, \(f(4)\) corresponds to the value of the hundreds digit of \(n\).) (1) \(f(1) = f(4), f(2) = f(5), f(3) = f(6)\)
The above condition implies that the last three digits of \(n\) are the same as the first three digits of \(n\). Therefore, \(n = abc,abc = abc*1000 + abc = abc*(1000 + 1) = abc*1001\). Since 1001 is divisible by 7 (1,001 = 143*7), then \(n = abc*1001\) must also be divisible by 7. Sufficient.
(2) \(f(1) = f(2) = f(3) = f(4) = f(5) = f(6)\)
The above condition implies that all digits of \(n\) are the same. Therefore, \(n = aaa,aaa = aaa*1000 + aaa = aaa*(1000 + 1) = aaa*1001\). Since 1001 is divisible by 7 (1,001 = 143*7), then \(n = aaa*1001\) must also be divisible by 7. Sufficient.
Answer: D