Q12: Despite the growing number of people who purchase plane tickets online, airline executives are convinced that, just as one-third of bank customers still prefer human tellers to automatic teller machines, many travelers will still use travel agents. A. growing number of people who purchase plane tickets online, airline executives are convinced that, just as one-third of bank customers still prefer human tellers to automatic teller machines, many travelers willB. growing number of people who purchase plane tickets online, airline executives are convinced, just as one-third of bank customers still prefer human tellers to automatic teller machines, that many travelers would C. growing number of people purchasing plane tickets online, airline executives are convinced, just as one-third of bank customers still prefer human tellers as compared to automatic teller machines, many travelers will D. fact that the number of people purchasing plane tickets online is growing, airline executives are convinced, just as one-third of bank customers still prefer human tellers as compared to automatic teller machines, that many travelers would E. fact that the number of people who purchase plane tickets online are growing, airline executives are convinced that, just as one-third of bank customers still prefer human tellers compared with automatic teller machines, many travelers would

问,A中airline executives are convinced that,是插入语吗?是什么结构?