Doubt about Mahabharata -- Good One

In a remote village of India, once masterji is teaching the Mahabharat katha to class 6 students. He is at the 'Krishna janma' part of it. Masterji: "Kansa heard the akashwani that his sister's 8th child is going to kill him. He was furious. He ordered to put Vasudev and Devki behind the bars. First son is born, and kansa kills him by poisoning... Second one is born n Kansa throws him off the mountain peak. Third one is born...
"Now Ramu, who is smartest of the lot, puts up his hand. Masterji, I have a doubt (sounding nervous and confused).


Masterji: "Ramu bete, whole India does not have doubt in mahabharata then how come you have one?"


Ramu: Masterji, if Kansa knew that Devaki's 8th child was going to Kill him, WHY THE HELL DID HE PUT VASUDEV AND DEVAKI IN THE SAME CELL?
Masterji fainted..... ....