Avatar or Expansion of Krishna: Vasudeva Krishna

                                                                  Q. In Chapter 4 beginning Krishna says that he instructed the imperishable science of yoga to sun god Vivsavan. I am curious as to which Avatar does this happened.

                                                                  A. Each time Krsna appears to deliver Bhagavad-gita, it is as Vasudeva Krsna.

                                                                   

                                                                  Q. A friend of mine said that Krishna never returned to Vrindavana after the battle of Kurukshetra. Yet, Caitanya-Caritamrta says that it was Vishnu who went to Mathura and that Krishna never leaves Vrindavana. Then there is Ratha Yatra, which is celebrating Krishna's return to Vrindavana. Could you please shed light on this?