Question 16 (1)△ABC, BD and CE are the center lines of AC and AB, and BD and CE intersect at O.

BO=2DO(BO is twice as much as DO),

The midline AF on the side of BC must pass through point O.

Prove: let OB midpoint m and OC midpoint n,

Even MN, ND, DE, EM,

By 200 BC, Germany was half that of BC,

MN‖BC, MN is half of BC,

∴DE‖MN, and DE=MN,

∴ quadrilateral EMND is a parallelogram.

The two diagonal lines MD and EN are equally divided,

∴OM=OD,∴BO=2DO，

Similarly: ON=OE,∴CO=2EO.

O is the center of gravity of triangle ABC,

∴AF is the midline of BC, which must pass through O.

(The intersection of the three midlines is the center of gravity of the triangle).