问题
选择题
若Sn是等差数列{an}的前n项和，且S8－S4＝12，则S12的值为( )
A．64
B．44
C．36
D．22
答案
答案：C
由S8－S4＝12得a5＋a8＝a6＋a7＝a1＋a12＝6，则S12＝
×(a1＋a12)＝36
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若Sn是等差数列{an}的前n项和，且S8－S4＝12，则S12的值为( )
A．64
B．44
C．36
D．22
答案：C
由S8－S4＝12得a5＋a8＝a6＋a7＝a1＋a12＝6，则S12＝×(a1＋a12)＝36
| 阅读理解。 | |
| |
| 1. On Sunday the zoo opens at ______. | |
[ ] | |
| A．10:00 in the morning B．8:00 in the morning C．6:00 in the afternoon D．8:00 in the afternoon | |
| 2. If you are 13, how much do you pay to go into the zoo? | |
[ ] | |
| A．3 dollars. B．6 dollars. C．8 dollars. D．Nothing. | |
| 3. Which of the following statements is true? | |
[ ] | |
| A．The zoo opens longer on Saturday and Sunday than on other days. B．Children under 8 can go into the zoo at any time without paying anything. C．Adults have to pay 17 dollars to go into the zoo. D．You can't take a train to the zoo on weekdays. | |
| 4. If Lucy is 14 and her brother is 7, how much do they pay for the train ride? | |
[ ] | |
| A．2 dollars. B．4 dollars. C．6 dollars. D．8 dollars. |