What determines what will be tested in a scientific experiment

This is the substance(s) formed in a chemical reaction.

The coefficient of friction is a number that represents the resistance to sliding between two in contact with one another.

Which of the following situations is impossible? a) an object has velocity directed east and acceleration directed east. b) an object has zero velocity but non-zero acceleration. c) an object has constant non-zero velocity and changing acceleration. d) an object has velocity directed east and acceleration directed west. e) an object has constant non-zero acceleration and changing velocity.