Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 34 to 40.

John McCarthy was often described as the father of 'artificial intelligence' (Al), a branch of computer science founded on the notion that human intelligence can be stimulated by machines. McCarthy, who coined the term in 1956, defined it as 'the science and engineering of making intelligent machines' and created the Lisp computer language to help researchers in the Al field. He maintained that there were aspects of the human mind that could be described precisely enough to be replicated: "The speeds and memory capacities of present computers may be insufficient to simulate many of the higher functions of the human brain," he wrote in 1955, "but the major obstacle is not lack of machine capacity but our inability to write programs taking full advantage of what we have."

McCarthy went on to create Al laboratories at the Massachusetts Institute of Technology, and later at Stanford University where he became the laboratory's director in 1965. During the 1960s he developed the concept of computer time-sharing, which allows several people to use a single, central, computer at the same time. If this approach were adopted, he claimed in 1961, "computing may someday be organized as a public utility". The concept of time-sharing made oossible the development of so-called "cloud computing" (the delivery of r.omputing as a service rather than a product). Meanwhile, his Lisp programming tanguage, which he invented in 1958, underpinned the development of voice recognition technology.

McCarthy taught himself mathematics as a teenager by studying textbooks at the California Institute of Technology. When he arrived at the Institute to study the subject aged 16, he was assigned to a graduate course. In 1948, a symposium sparked his interest in developing machines that can think like people. McCarthy received a doctorate in Mathematics from Princeton University in 1951 and was immediately appointed to a Chair in the subject. It was at Princeton University that he proposed the programming language Lisp as a way to process more sophisticated mathematical concepts that Fortran, which had been the dominant programming medium until then. McCarthy joined the Stanford faculty in 1962, remaining there until his official retirement in 2000.

During the 1970s he presented a paper on buying and selling by computer. He also invited a local computer hobby group, the Homebrew Computer Club, to meet at the Stanford laboratory. Its members included Steve Jobs and Steven Wozniak, who would go on to found Apple. However, his own interest in developing time-sharing systems led him to underestimate the potential of personal computers. When the first PCs emerged in the 1970s, he dismissed them as "toys". Despite his disappointment with Al, McCarthy remained confident of the power of mathematics: "He who refuses to do arithmetic is doomed to talk nonsense," he wrote in 1995.

The word "obstacle" in paragraph 1 is closest in meaning to _______ A. advantage B. challenge C. description D. report