—________
A:That is Jane.
B:This is Kangkang speaking.
C:I'm Mike.
D:She is Maria.
如图,直线L1,L2交于一点P,若y1≥y2,则x的取值范围是____
如图,在△ABC中,∠ACB=90°,BC的垂直平分线DE交BC于D,交AB于E,F在DE上,并且AF=CE.
(1)求证:四边形ACEF是平行四边形;
(2)当∠B满足什么条件时,四边形ACEF是菱形?请回答并证明你的结论.