Complete sentence:
On colliding, the truck applies a force on the stationary car, and the stationary car applies -An equal- . and opposite force on the truck. The front of the truck is designed to crumple in order to - Lower the force of impact, which protects the well-being of the passengers.
Step-by-step explanation:
The first part - an equal - is a result of Newton's third law, which states that:
"When an object A exerts a force on an object B, then object B exerts an equal and opposite force on object A". In this particular case, the two objects are the truck and the car, so when the truck exerts a force on the car, the car exerts an equal and opposite force on the truck.
The front of the truck is designed to crumple, so that the time of the collision becomes longer: this way, the deceleration of the truck becomes smaller, as given by the equation

And therefore, the force on the truck becomes smaller, as given by Newton's second law:

if the acceleration is smaller, than the force is smaller.