题干
So serious ________ that even the best doctors failed to save his life.
A：the man was injured
B：was the man injured
C：the man is injured
D：is the man injured
答案(点此获取答案解析）
B
的图象如图1所示，它在定义域上是减函数，给出如下命题：①
=1；②
；③若
，则
；④若
，则
，其中正确的是（ ）