In what now seems like the prehistoric times of computer history, the early post-war era(战后时期), there was a quite widespread concern that computers would take over the world from man one day. Already today, less than forty years later, as computers are relieving us of more and more of the routine tasks in business and in our personal lives, we are faced with a less dramatic but also less foreseen problem People tend to be over-trusting(过分信任) of computers and are reluctant to challenge their authority. Indeed, they behave as if they were hardly aware that wrong buttons may be pushed, or that a computer may simply malfunction(失灵).
Obviously, there would be no point in investing(投入) in a computer if you had to check all its answers, but people should also rely on their own internal computers and check the machine when they have the feeling that something has gone wrong. Questioning and routine double checks must continue to be as much a part of good business as they were in pre-computer days. Maybe each computer should come with the following warning: for all the help this computer may provide, it should not be seen as a substitute for fundamental thinking and reasoning skills.
What is the main purpose of this passage？

A. To look back to the early days of computers.
B. To explain what technical problems may occur with computers.
C. To discourage unnecessary investment in computers.
D. To warn against the blindness to the probable shortcomings of computers.