Chọn câu đúng \(a\frac{a}{{99}} = \frac{{100{\rm{a}}}}{{99}}\,\,\left( {a \in {N^*}} \right)\)

A. \(\frac{{19.20}}{{19 + 20}} = \frac{1}{{19}} + \frac{1}{{20}}\)

B. \(6\frac{{23}}{{11}} = \frac{{6.23 + 11}}{{11}}\)

C. \(a\frac{a}{{99}} = \frac{{100{\rm{a}}}}{{99}}\,\,\left( {a \in {N^*}} \right)\)

D. \(\frac{{15}}{{23}} = \frac{{1.23}}{{15}}\)