In a right triangle, angle $A$ is acute. The side opposite $A$ has length $a$, the side adjacent to $A$ has length $b$, and the hypotenuse has length $c$. Which expressions give $sinA$ and $cosA$?

• A. $sinA=\frac{c}{a},cosA=\frac{c}{b}$
• B. $sinA=\frac{a}{b},cosA=\frac{c}{b}$
• C. $sinA=\frac{b}{c},cosA=\frac{a}{c}$
• D. $sinA=\frac{a}{c},cosA=\frac{b}{c}$

Answer: (D)