任取x₁，x₂∈a，b，且x₁≠x₂，若$f\left(\frac{x_1+x_2}{2}\right)>\frac{1}{2}f\left(x_1\right)+f\left(x_2\right)$，称f（x）是a，b上的凸函数，则下列图象中，是凸函数图象的是（　　）

   Jack went to a barber’s shop and had his hair cut, but when he came out, he was not  h____  with the result. When his friend Bob saw him, he  l____  and said, “What happened to your hair, Jack?”
   Jack said, “I tried a new barber’s shop today, because I wasn’t quite satisfied with the  o____  one, but this one seems even w____ .”
   Bob agreed. “Yes. I think you are right, Jack. Now I’ll tell you  w____  to do when you go into a barber’s shop  n____  time. Look at the barber’s hair, find out whose hair  l____  worst, and then go straight to him.”
   “Why shall I go to him?” Jack asked, “But that would be foolish.”
   “Oh, no, it wouldn’t.” said Bob. “Who cut that man’s  h____ ? Just think it over. He couldn’t cut it   h____ , could he? One of the  o____  barbers cut it. So you know he can’t be the worst barber.”

20世纪90年代，陕西章台出土了一些封泥，上面有上郡、代郡、邯郸等郡名和蓝田等县名。这些文物最早出现于（     ）

读图，回答下列问题。