题目: 11×2+12×3+13×4+14×5+15×6+16×7+17×8. 答案: 11×2+12×3+13×4+14×5+15×6+16×7+17×8=(1-12)+(12-13)+…+(17-18),=1-18,=78;
题型:选择题 — How old is your son? — _____. We had a special party for his _____ birthday last Sunday. A. Nine; nine B. Nine; ninth C. Ninth; ninth D. Ninth; nine 查看答案