利用植物的叶片、茎尖、花药等，在无菌的条件下培养，使它们发育成完整的植株。这种技术可以在短时间内大量繁殖植物。下列关于这种技术的叙述，正确的是(　　)
①这种技术利用了植物细胞的全能性　②这种技术是一种无性繁殖方式　③这种技术可以防止病毒对植物的危害　④这种技术可以培育植物新品种

五氧化二钒(V₂O₅)中钒元素的化合价为  

任务型阅读

   ①The meaning of shaking the head is not always the same in different countries. Maybe some visitors would be surprised when they first came to India. When talking to an Indian, he would often shake his head. The visitors might think that the Indian did not like what they said. But, in fact, they would be completely(完全地)wrong.

   Indians always shake their heads when they talk to each other. It does not have the same meaning as“No”. If someone wants  ②  (visit)India, he should know this, or it will give him some trouble.

   One day, a foreign officer went to  ③  on business. He leased(租用)a car and hired(雇用)an Indian to drive it. When he told his driver to send him to his office, the Indian shook his head at once. The officer said again, and the driver shook his head again. At last, the officer, of course, got angry.

   “Why do you refuse(拒绝)my order(要求)? ”he shouted. “Drive me to my office at once! ”

   The driver answered in a quite loud voice, too. “Yes, sir! ”But to the officer’s surprise, the driver shook his head at the same time.

The car started, and the foreign officer was now too surprised to say a word. He thought about it for a while, and then ④he nodded with a smile, “‘No’ means ‘Yes’ here! ”

正如当初无人能预测1450年的印刷术、1750年的蒸汽机、1950年的晶体管会带来何等影响，而今我们仍然无法预测3D打印将在未来漫长的时间里如何改变世界。这说明（   ）