Answer:
D. 23x^9-12x+19
Step-by-step explanation:
Standard form of a polynomial starts with largest exponent and then exponent decreases
A. 2x^4+6+24^x
It is not a polynomial because it has exponent x
B. 6x^2-9x^3+12x^4
It is not in standard form because first term is x^2 (smallest exponent)
C. 19x+6x^2+2
It is not in standard form because the exponents are increasing
D. 23x^9-12x+19
It is in standard form because the exponents are decreasing