Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 18 to 22.

A scientist said robots will be more intelligent than humans by 2029. The scientist's name is Ray Kurzweil. He works for Google as Director of Engineering. He is one of the world's (18) ______ experts on artificial intelligence (A.I.). Mr Kurzweil believes computers will be able to learn from experiences, just like humans. He also thinks they will be able to tell jokes and stories, and even flirt. Kurzweil's 2029 prediction is (19) ______ sooner than many people thought. The scientist said that in 1999, many A.I. experts said it would be hundreds of years before a computer was more intelligent than a human. He said that it would not be long before computer intelligence is one billion times more powerful than the human brain. Mr Kurzweil joked that many years ago, people thought he was a little crazy (20) ______ predicting computers would be as intelligent as humans. His thinking has (21) ______ the same but everyone else has changed the way they think. He said: "My views are not radical any more. I've actually stayed consistent. It's the (22) ______ of the world that's changing its view." He highlighted examples of high-tech things we use, see or read about every day. These things make us believe that computers have intelligence. He said people think differently now: "Because the public has seen things like Siri [the iPhone's voice-recognition technology] where you talk to a computer; they've seen the Google self-driving cars." 

He is one of the world's (18) ______ experts on artificial intelligence (A.I.)