(1) AC∨MN can be known from the proportion of parallel lines, and AC∨ plane MNP can be obtained from the judgment of parallel lines and planes, which can also prove BD∨ plane MNP;

(2) Take point Q on AD and make CP: PD = AQ: QD, which can prove that PQ is the intersection of plane MNP and plane ACD. It is easy to prove the conclusion by dividing the line segments in proportion with parallel lines.

Solution: Solution: (1) From the meaning of the question AM: MB = CN: NB, we can know from the proportion of parallel lines: AC∨MN,

Is it because of MN again? The plane MNP, AC got out of the plane MNP,

From the judgment theorem of line-plane parallelism, we can get the following: AC∑ plane MNP,

Similarly, BD∑NP can be obtained from cn: nb = CP: PD,

Because BD is out of plane and NP is in plane, there is BD∑ plane MNP；; ;

(2) Take point Q on AD to make CP: PD = AQ: Qd,

According to the proportion of parallel lines, PQ∨AC, AC∨MN from (1),

So PQ∨MN, so PQ? Plane MNP, PQ again? Aircraft ACD,

So PQ is the intersection of plane MNP and plane ACD, and it can be known from PQ∑AC.

Intersection of plane MNP and plane ACD∑AC.

Comments: This question is a proof of parallelism between lines and planes. Pay attention to the two lines inside and outside the plane, which is the key to prove that the lines and planes are parallel.

I hope the landlord will adopt it and wish the landlord a happy new year!