Make a height line first, and then use the height of the trapezoid and the upper and lower bottoms to represent the triangle area, and then you can make a judgment.

Answer: solution: a, ∫AD∨BC

∴△AOD∽△BOC

S 1=AD？ OE, S2 = BC? Yes, S3 = A.D.? EF = AD(OE+OF)-s 1 = AD(OE+OF)-AD？ OE=AD？ Yes,

S4 = BC? EF=BC(OE+OF)-S2=BC(OE+OF)-BC？ OF=BC？ Old English

∴S 1？ S2 = A.D.? OE？ BC? S3? S4 = A.D.? Yes? BC? Old English

∴S 1×S2=S3×S4

Comments: This question mainly examines the judgment and nature of trapezoid and similar triangles. Correctly representing the area of each triangle is the key.