Trouble with making a smooth position transition

[fongw81734131]

I am trying to make a very simple position transition as below:

Animate an object from point A to B and then back to point C a bit. After set up those keyframes, I found the animation is not smooth, so I opened the value graph and found: 

There is a "tail" after point B, so I am wondering how can make it smoother?

More reference, the speed graph is like this: 

Thank you very much for you guys help! 

[Mylenium]

The answer is pretty obvious even if you did not select any points to show the tangents: These are tangent kinks because the incoming tangent of point C is wayy too far extended and interferes with point B's out-tangent. You need to tweak that stuff suitably or add an extra inbetween keyframe if necessary.

Mylenium