下列选项中的四边形只有一个为平行四边形，根据图中所给的边长长度及角度，判断哪一个为平行四边形？（　　）

    More than 6000 children were expelled（开除）from US schools last year for bringng guns and bombs to school，the US Department of Education said on May 8．
    The department gave a report on the expulsions（开除）as saying handguns accounted for 58 per cent of the 6093 expulsions in 1996—97，against 7 per cent for rifles or shotguns and 35 per cent for other types of firearms．
    “The report is a clear sign that our nation’s public schools are cracking down（严惩）”on students who bring guns to school，“Education Secretary Richard Riey said in a statement．“We need to be tough-minded（坚强的）about keeping guns out of our schools and do everything to keep our children safe．”
    In March 1997，an 11-year-old boy and a 13-year-old using hand-guns and rifles shot dead four children and a teacher at a school in Jonesboro，Arkansas．In October，two were killed and seven wounded in a shooting at a Mississippi school．Two months later，a 14-year-old boy killed three high school students and wounded five in Daducab，Kentucky．
    “Most of the expulsions，56 per cent，were from high schools，which have students from about age 13，34 per cent were from junior high schools and 9 per cent were from elementary schools．”The report said．

一理想变压器给负载供电，变压器输入电压不变，如图所示．如果负载电阻的滑动片向上移动，则图中所有交流电表的读数及输入功率变化情况正确的是（均为理想电表）（   ）