Answer:
The expression -7x^0 cannot be a part of a rational expression because any non-zero number raised to the power of 0 is equal to 1. Therefore, -7x^0 is equal to -7(1) = -7, which is a constant and not a variable expression. In a rational expression, the numerator and denominator should be polynomial expressions with variables.
The other options 4, 3x^2-4rootx, and 3x^2-4x+5 can be part of a rational expression as they are polynomial expressions with variables.