题干
For now, I have to stay at home because of my illness.
A：At present
B：For example
C：As for me
答案(点此获取答案解析）
A
For now, I have to stay at home because of my illness.
A：At present
B：For example
C：As for me
在平面
内，并且对空间任一点
，
则
的值为（ ）