已知等差数列{an}中，a7+a9=16,a4=1，则a12的值是（）

题干

已知等差数列{a_n}中，a7+a9=16,a4=1，则a12的值是（）

A：15

B：30

C：31

D：64

上一题下一题 0.0难度选择题更新时间:2014-07-03 01:49:34

A

This Sunday is grandpa's birthday. The Smith family are going to celebrate it at home, so they will have a busy weekend.

Saturday
Morning	Dad-clean the car in the garden Mum-clean the kitchen and bedrooms of their house Amy-have dance lessons in the gym Rose--work on science projects in the library
Afternoon	Mum and Dad-buy some food at the supermarket Amy and Rose-choose gifts and cards for grandpa
Evening	Watch TV together
Sunday
Morning		Mum---make a big birthday cake Amy and Rose-wrap grandpa's gifts
Afternoon		Amy-help Mum cook delicious food Rose-help Dad decorate the sitting room
Evening		Amy and Rose-give gifts to grandpa The whole family-have a party

根据表格所提供信息，从每小题所给的A、B、C三个选项中，选出一个最佳答案。