As per definition of inertia we know that it is the property of mass which resist any change in the state of motion.
So if the object is moving in certain direction then it will continue in the same direction with same velocity until some external force will act upon it.
Here when force object is in infinite space then there is no force on that object so it will continue to move in the same direction with same velocity because of the property of inertia.
So here the motion remains in straight line without any change in the direction due to inertia of the body
A. because none of the other answers make sense, there is no air in space, acceleration would change the velocity, force would imply something moved it which is highly unlikely (unless we are talking about starwars), and inertia is a tendency to do nothing or to remain unchanged or a property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force.
