问题
选择题
It rained a lot during their journey, so they _____ have had a good time. [ ]
A. can't
B. must
C. shouldn't
D. might
答案
答案：A
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It rained a lot during their journey, so they _____ have had a good time. [ ]
A. can't
B. must
C. shouldn't
D. might
答案：A
| 数学家高斯在上学时曾经研究过这样一个问题，1+2+3+…+10=？ 经过研究，这个问题的一般性结论是1+2+3+…+n=
观察下面三个特殊的等式： 1×2=n（1×2×3-0×1×2） 2×3=x（2×3×4-1×2×3） 3×4=n（3×4×5-2×3×4） 将这三个等式的两边相加，可以得到1×2+2×3+3×4=m×3×4×5=20． 读完这段材料，请你计算： （1）1×2+2×3+…+100×101=______；（直接写出结果） （2）1×2+2×3+…+n（n+1）；（写出计算过程） （3）1×2×3+2×3×4+…+n（n+1）（n+2）=______． |