SECTION ADirections: Beneath each of the following sentences there are 4 choices marked A,B,C and D. Choose the one answer that best completes the sentence.
    21．Travelers        that they should bring their ID cards with them.
    A．have remindedB．are remindedC．were remindingD．had been reminded22．---The authors of computer viruses are geniuses.
    ---I agree. They can apply their wisdom to other net technology from     human beings can benefit.