在探究凸透镜成像规律的实验中，当烛焰、凸透镜、光屏处于如图所示的位置时，恰能在光屏上得到一个清晰的像．利用这一成像原理的光学仪器是（  ）

学习，对每个人来说都是苦乐交织的，学习的快乐在于（   ）
①了解奥秘后的满足  ②发现进步后的快乐   ③攻克难题后的喜悦   ④艰辛探究后的幸福

在△ABC中，若$\sin A=\frac{1}{2}$，tanB=1，则这个三角形是（   ）

   This is a picture of Mr Black's family. The man is Mr Black. The woman is Mrs Black. They have a son and a daughter. The son is behind Mr Black. He looks like his mother. His name is Mike. He's thirteen. Their daughter, Ann is behind Mrs Black. She is eleven. Mike and Ann are in the same school. But they are not in the same grade. Mike is in Grade Nine. Ann is in Grade Seven. They are good students at school. Mike likes English, but he doesn't like math. Ann likes Chinese and math. She also likes singing English songs.
根据短文内容完成下列句子，每空一词。

在实验设计中，下列哪个选项不能作为一组对照实验（  ）