题目内容：
Agriculture is the country's chief source of wealth, wheat __________ by far the biggest cereal crop.
A．is B．been
C．be
D．being
参考答案：
答案解析：
单选题：Agriculture is the country's chief source of wealth, wheat _
- 题目分类：专四
- 题目类型：单选题
- 查看权限：VIP
B．been
C．be
D．being