如图，在⊙O中，AC与BD是圆的直径，BE⊥AC，CF⊥BD，垂足分别为E、F

（1）四边形ABCD是什么特殊的四边形？请判断并说明理由；

（2）求证：BE=CF．

    There are ten books about English. They are on Shelf D. There are seven books about music. They are on Shelf B. There are nine books about computers. They are on Shelf C. There are five books about art. They are on Shelf A.

⑴Books about English____       A. nine      a. Shelf A

⑵Books about music____        B. seven     b. Shelf B

⑶Books about computers____   C. five       c. Shelf C

⑷Books about art____           D. ten       d. Shelf D

下列做法属于减小摩擦的是（  ）