Solution: solution; A, after the object is in contact with the spring, the object is subject to elastic force, but the elastic force is less than the initial thrust, and the object continues to accelerate until the elastic force equals the thrust, so A is wrong.

B, after the object is in contact with the spring, the object is elastic, but at first the elastic force is less than the thrust, and the object continues to accelerate until the elastic force equals the thrust, so B is wrong.

C, after contacting the spring, the object has elasticity, but at the beginning, the elasticity is less than the thrust, and the object continues to accelerate. When the elastic force increases to equal the thrust, the speed of the object reaches the maximum, so C is correct.

D, when the spring is in maximum compression, the speed is zero, the elastic force is greater than the thrust, so the resultant force is not zero, and the acceleration is not zero, so D is wrong.

So choose C.