What immediately caught my attention with #6 was the one arrow with two circles near it. In the cases of B, C, and D...it became pretty clear to me that the two circles would position themselves behind and to the left of the one arrow. When I looked at A, it became fairly obvious that the position of the "left" circle would actually be on the right of either of the arrows, and that the "left" position was going to be occupied by a square instead. Here's a picture of it with some lines to show you what I mean.