The expression \( x - 4y^3 \) does not simplify further into a single fraction or change forms, as it is already in its simplest polynomial form.
However, if we interpret the request in terms of expressing it as a fraction (to clarify the options):
- To express \( x - 4y^3 \) as a fraction, it could be represented as: \[ \frac{x - 4y^3}{1} \] This still does not match exactly with any options.
Given the options:
- \( \frac{1}{x^4y^3} \)
- \( \frac{x^4}{y^3} \)
- \( \frac{y^3}{x^4} \)
- \( -x^4y^3 \)
The correct response based on the expression provided would be that none of these options are accurate representations or simplifications of the expression \( x - 4y^3 \).
If we are to relate any of these options back towards the form of an expression, the answer is simply not applicable. Therefore, the answer would be a choice of not selecting any of the provided options.