OG详解-OG7 数学2 Q10

Choice D is correct. The given expression can be rewritten as (9x³ +6x³)+5x² +5x+(7-5). Combining like terms in this expression yields 15x³ +5x² +5x+2.
Choice A is incorrect and may result from conceptual or calculation errors. Choice B is incorrect and may result from conceptual or calculation errors. Choice C is incorrect and may result from conceptual or calculation errors.