Simplify the expression (2 t + 2 t)/2 t and choose the correct option.

The Pythagorean identity states that $\sin^2 t + \cos^2 t = 1$.
Substitute this into the numerator of the expression:

$$\frac{\sin^2 t + \cos^2 t}{\sin^2 t} = \frac{1}{\sin^2 t}$$

The reciprocal identity for sine states that $\csc t = \frac{1}{\sin t}$.
Therefore, $\csc^2 t = \left(\frac{1}{\sin t}\right)^2 = \frac{1}{\sin^2 t}$.
So, the expression simplifies to:

$$\frac{1}{\sin^2 t} = \csc^2 t$$

Comparing this result with the given options:
A) $\sin^2 t$
B) $\cos^2 t$
C) $\tan^2 t$
D) $\csc^2 t$

The simplified expression matches option D.

The final answer is \boxed{\text{D) \csc^2 t}}.