In right triangle $\Delta ABC$, assume the right angle is at $C$. Which expression is equivalent to $\sin \left(A\right)$?

Given a right triangle where angle $A$ measures $39°$ and side $\mathrm{BC}$ is the hypotenuse, what is the measure of arc $\mathrm{BC}$ in degrees?

Given a right triangle with hypotenuse of length $c$ and an acute angle $\theta$, express the lengths of the side adjacent to $\theta$ (labeled $a$) and the side opposite $\theta$ (labeled $b$) in terms of $c$ and $\theta$.

Given a right triangle where one of the acute angles is $\theta$, and the side opposite $\theta$ has length $3$, the side adjacent to $\theta$ has length $4$, and the hypotenuse has length $5$, what are the exact values of the six trigonometric ratios for angle $\theta$?