问题
选择题
等差数列{an}的前项和为Sn,若a2=1,a3=3,则S4= |
A.12 B.10 C.8 D.6 |
答案
答案:C
等差数列{an}的前项和为Sn,若a2=1,a3=3,则S4= |
A.12 B.10 C.8 D.6 |
答案:C
Do you remember your home phone number or family birthday? The researchers(调查者)spent two weeks polling(调查)4,000 people for the magazine named Brain Trainer. Here are the results of the survey.
The survey took the researchers about half a 小题1:_________. From the survey, we know lots of people 小题2:_ ________ remember their home phone numbers or 小题3:_________ because they always use their 小题4:_________ to remember them. Most people rely on electronic tools instead of 小题5:_______ important dates themselves. Without electronic tools, can you imagine what your life will be like? |