Concept: Simplify by expanding the bracket first, then combining like terms.Explanation:Start with the expression 4a−9b−2(2a−3b).Expand the bracket: −2(2a−3b)=−4a+6b.So the expression becomes 4a−9b−4a+6b.Group like terms: (4a−4a)+(−9b+6b).This simplifies to 0a−3b=−3b.Answer: D. −3b