It is helpful if you stop and think what are the strengths and weaknesses of your research and your method.（ ） A. 对 B. 错

（ ）一般不单独使用，常与轨道遮罩、差值遮罩等其他键控方式相结合，用来调整透明和不透明部分的交界线，扩大或缩小...

单项选择题（ ）一般不单独使用，常与轨道遮罩、差值遮罩等其他键控方式相结合，用来调整透明和不透明部分的交界线，扩大或缩小透明区域的范围，移除其他键控效果没有抠除干净的背景部分，所以该方式一般在轨道遮罩或差值遮罩之后使用。 A. Alpha调整 B. 图像遮罩键 C. 移除遮罩 D. 差值遮罩

Why did printing become possible? A、Because Chinese ...

单项选择题Why did printing become possible? A、Because Chinese people were very hard-working. B、Because Chinese people learned that from the westerners. C、Because of the invention and improvement of papermaking. D、Because Chinese government sent many people to study that.

(  )A.B.C.D.

单项选择题(  ) A. B. C. D.