Given the function \( d(t) = 50t \), the variable \( t \) represents the following:
- Input: \( t \) is the value we provide to the function to calculate \( d(t) \).
- Independent variable: \( t \) is independent because it can take any value, and it determines the value of \( d(t) \).
The other options do not apply to \( t \):
- Dependent variable: This would be \( d(t) \) since its value depends on \( t \).
- Function: The function itself is \( d(t) \), not \( t \).
- Output: This also refers to \( d(t) \), as it is the output of the function when \( t \) is input.
Therefore, the correct answers are input and independent variable.