The sum of (a2−1) and (a+1) can be rewritten as (a2−1)+(a+1), or a2−1+a+1, which is equal to a2+a+0. Therefore, the sum of the two expressions is equal to a2+a. Choices B and D are incorrect. Since neither of the two expressions has a term with a3 the sum of the two expressions cannot have the term a3 when simplified. Choice C is incorrect. This choice may result from mistakenly adding the terms a2 and a to get 2a2