题目

 Last year, a special kind of glove came out. It was invented to help blind people to learn Braille, which is a special system for the blind to read by touching. Shaking motors (震动马达) are put on each finger of the glove. They can make different sounds to tell a user which letter he is touching. Recently, two British college students have invented another special glove for the blind. It can make the user feel small and quick movements. An ultrasonic sensor(超声波传感器)with a battery is put on the back of the glove. When the user wearing the glove is close to an obje玉米干旱缺水时叶片的内卷主要是    失水造成的(单选1分)     A、叶肉细胞            B、叶表皮的毛状体     C、位于上表皮的泡状(运动)细胞      D、位于下表皮的泡状(运动)细胞