詳解：(A)  \(\angle A:\angle B:\angle C = \frac{1}{6}:\frac{2}{6}:\frac{3}{6}\)

\(\frac{1}{6} \cdot {180^ \circ } = {30^ \circ }\quad \frac{2}{6} \cdot {180^ \circ } = {60^ \circ }\quad \frac{3}{6} \cdot {180^ \circ } = {90^ \circ }\)

(B) \(\angle A:\angle B:\angle C = \frac{2}{9}:\frac{3}{9}:\frac{4}{9}\)

\(\frac{2}{9} \cdot {180^ \circ } = {40^ \circ }\quad \frac{3}{9} \cdot {180^ \circ } = {60^ \circ }\quad \frac{4}{9} \cdot {180^ \circ } = {80^ \circ }\)

(C) \(\angle A:\angle B:\angle C = \frac{3}{{12}}:\frac{4}{{12}}:\frac{5}{{12}}\)

\(\frac{3}{{12}} \cdot {180^ \circ } = {45^ \circ }\quad \frac{4}{{12}} \cdot {180^ \circ } = {60^ \circ }\quad \frac{5}{{12}} \cdot {180^ \circ } = {75^ \circ }\)

(D) \(\angle A:\angle B:\angle C = \frac{4}{{15}}:\frac{5}{{15}}:\frac{6}{{15}}\)

\(\frac{4}{{15}} \cdot {180^ \circ } = {48^ \circ }\quad \frac{5}{{15}} \cdot {180^ \circ } = {60^ \circ }\quad \frac{6}{{15}} \cdot {180^ \circ } = {72^ \circ }\)

(A)為直角 \(\Delta \)