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Answer:
D. -31m^4n-8m^2
Step-by-step explanation:
Eliminate parentheses by distributing the minus sign. Then collect terms:
(9mn-19m^4n)-(8m^2+12m^4n+9mn) = 9mn -19m^4n -8m^2 -12m^4n -9mn
= m^4n(-19 -12) +mn(9 -9) +m^2(-8)
= -31m^4n -8m^2 . . . . . matches choice D
