This one's easier than you think.
For E2 reactions, where do you deprotonate?
From the anti-coplanar side. And the more exposed that Hydrogen is, without any bulky group being all up in its face, the better.
Choice B is good because the I is facing the same side as the Huge trimethyl, so that means the Hydrogen that will be deprotonated will be from the back side facing behind.
I know, Destroyer's explanation is a bit over the head WOOSH~~~
