As shown in the figure, if the straight line EF passes through the intersection o of diagonal lines of parallelogram ABCD and intersects AB, CD at e and f respectively, the area of the shadow part is () A. 15B. 14C. 13D. 12

∵ quadrilateral ABCD is a parallelogram, ∵ OA = OC, OB = OD, ab ‖ DC, ≌ AOE ≌ COF, ≌ s △ AOE = s △ COF, ∤ AOD = ≌ cob, ≌ cob ≌ AOD, ≌ s △ AOD = s △ BOC

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1. As shown in the figure, in the isosceles ladder ABCD, ad ‖ DC, ab = DC, diagonal AC and BD intersect at point O, Bo = 6cm, e is a moving point on the edge of BC (point E does not coincide with B and C), EF ‖ BD intersects AC at point F, eg ‖ AC intersects BD at point g. during the movement of point E, try to guess whether the sum of the lengths of GH and EF changes? If so, explain your reason; if not, request its value
2. As shown in the figure, in ladder ABCD, ad is parallel to BC, ad is less than BC, ab = DC, AC, BD intersect at point O, the angle BOC = 60 degrees, e, F, G are the midpoint of Ao, Bo, DC respectively, prove that the triangle EFG is an equilateral triangle
3. In trapezoidal ABCD, ad ‖ BC, ab = DC, AC, BD intersect with point O, and ∠ BOC = 60 ° Find the length of EF If e and F are the midpoint of OC and ab respectively, ad = 1 and BC = 2,
4. The diagonals AC and BD of parallelogram ABCD intersect at point O, BF passes through point O, and intersect with AB and CD at points E and f respectively After modification: the diagonal lines AC and BD of parallelogram ABCD intersect at point O, EF passes through point O, and intersects with AB and CD at points E and f respectively
5. As shown in the figure, in trapezoidal ABCD, ad ∥ BC, diagonal AC and BD intersect vertically at O, Mn is the median line of trapezoidal ABCD, ∠ DBC = 30 °, verification: AC = Mn
6. As shown in the figure, in trapezoidal ABCD, ad ∥ BC, diagonal AC and BD intersect vertically at O, Mn is the median line of trapezoidal ABCD, ∠ DBC = 30 °, verification: AC = Mn
7. As shown in the figure, in trapezoidal ABCD, ad ∥ BC, diagonal AC and BD intersect vertically at O, Mn is the median line of trapezoidal ABCD, ∠ DBC = 30 °, verification: AC = Mn
8. As shown in the figure, M is a point on the side ad of the parallelogram. If the area of the parallelogram ABCD is four square centimeters, what is the area of the triangle MBC
9. Trapezoid ABCD, M is the waist midpoint of AD, triangle ABM area is 8, triangle MCD is 12, calculate the area of triangle BMC
10. M is a point on parallelogram ad. if the area of parallelogram ABCD is equal to 4 square centimeters, how many square centimeters is the area of triangle MBC equal to?
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16. The trapezoid's upper bottom is increased by 3 cm, and the lower bottom is increased by 2.5 cm to form a square with a circumference of 36 cm
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