The geese that gather at the pond of a large corporation create a hazard for executives who use the corporate helicopter, whose landing site is 40 feet away from the pond. To solve the problem, the corporation plans to import a large number of herding dogs to keep the geese away from the helicopter.
Which of the following, if a realistic possibility, would cast the most serious doubt on the prospects for success of the corporation’s plan

A．The dogs will form an uncontrollable pack.

B．The dogs will require training to learn to herd the geese.

C．The dogs will frighten away foxes that prey on old and sick geese.

D．It will be necessary to keep the dogs in quarantine for 30 days after importing them.

E．(E) Some of the geese will move to the pond of another corporation in order to avoid being herded by the dogs.

在PLC中，可以通过编程器修改或增删的是（）。

A、系统程序

B、用户程序

C、工作程序

D、任何程序